Replace all instances of XXXXXXXXXXXX with your own aws account id, then attach this policy to groups where you want MFA enforced

AwsEnforceMfaPolicy.json

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AllowAllUsersToListAccounts",
            "Effect": "Allow",
            "Action": [
                "iam:ListAccountAliases",
                "iam:ListUsers",
                "iam:GetAccountSummary"
            ],
            "Resource": "*"
        },
        {
            "Sid": "AllowIndividualUserToSeeAndManageOnlyTheirOwnAccountInformation",
            "Effect": "Allow",
            "Action": [
                "iam:ChangePassword",
                "iam:CreateAccessKey",
                "iam:CreateLoginProfile",
                "iam:DeleteAccessKey",
                "iam:DeleteLoginProfile",
                "iam:GetAccountPasswordPolicy",
                "iam:GetLoginProfile",
                "iam:ListAccessKeys",
                "iam:UpdateAccessKey",
                "iam:UpdateLoginProfile",
                "iam:ListSigningCertificates",
                "iam:DeleteSigningCertificate",
                "iam:UpdateSigningCertificate",
                "iam:UploadSigningCertificate",
                "iam:ListSSHPublicKeys",
                "iam:GetSSHPublicKey",
                "iam:DeleteSSHPublicKey",
                "iam:UpdateSSHPublicKey",
                "iam:UploadSSHPublicKey",
                "iam:ListUserPolicies",
                "iam:GetUser",
                "iam:ListGroupsForUser",
                "iam:ListUserTags",
                "iam:ListServiceSpecificCredentials"
            ],
            "Resource": "arn:aws:iam::XXXXXXXXXXXX:user/${aws:username}"
        },
        {
            "Sid": "AllowIndividualUserToListOnlyTheirOwnMFA",
            "Effect": "Allow",
            "Action": [
                "iam:ListVirtualMFADevices",
                "iam:ListMFADevices"
            ],
            "Resource": [
                "arn:aws:iam::XXXXXXXXXXXX:mfa/*",
                "arn:aws:iam::XXXXXXXXXXXX:user/${aws:username}"
            ]
        },
        {
            "Sid": "AllowIndividualUserToManageTheirOwnMFA",
            "Effect": "Allow",
            "Action": [
                "iam:CreateVirtualMFADevice",
                "iam:DeleteVirtualMFADevice",
                "iam:EnableMFADevice",
                "iam:ResyncMFADevice"
            ],
            "Resource": [
                "arn:aws:iam::XXXXXXXXXXXX:mfa/${aws:username}*",
                "arn:aws:iam::XXXXXXXXXXXX:user/${aws:username}*"
            ]
        },
        {
            "Sid": "AllowIndividualUserToDeactivateOnlyTheirOwnMFAOnlyWhenUsingMFA",
            "Effect": "Allow",
            "Action": [
                "iam:DeactivateMFADevice"
            ],
            "Resource": [
                "arn:aws:iam::XXXXXXXXXXXX:mfa/${aws:username}*",
                "arn:aws:iam::XXXXXXXXXXXX:user/${aws:username}*"
            ],
            "Condition": {
                "Bool": {
                    "aws:MultiFactorAuthPresent": "true"
                }
            }
        },
        {
            "Sid": "BlockAnyAccessOtherThanAboveUnlessSignedInWithMFA",
            "Effect": "Deny",
            "NotAction": "iam:*",
            "Resource": "*",
            "Condition": {
                "BoolIfExists": {
                    "aws:MultiFactorAuthPresent": "false"
                }
            }
        }
    ]
}