credits.js

.then((details) => {
    const newDetails = _.merge(details, {
        creditLines: _.map(credit => {
            if (!credit.creditTransaction) { return credit; }
            
            const taxCredit = parseFloat(credit.creditTransaction.taxAmount, 10);
            const tax = parseFloat(credit.originalTransaction.taxAmount, 10);
            const lineTotal = parseFloat(credit.creditTransaction.lineTotal, 10);
            
            return _.merge(credit, {
                lineTotal: lineTotal - tax - taxCredit
            });
        }, details.creditLines)
    });

    this.dispatch(ActionTypes.billing.CREDIT_DETAIL, [
        originalTransactionId,
        newDetails
    ]);

    return newDetails;
});