Stockholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Class of Stock [Line Items]
Net interest revenue	$ (512)	$ (546)
Total reclassifications out of AOCI	(319)	(373)
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Total reclassifications out of AOCI	4	5
Net Unrealized Gains (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Tax on derivatives qualifying as hedges	0	0
Net Unrealized Gains (Losses) on Available-for-Sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net gains (losses) from sales of available-for-sale securities	3	0
Tax on investments, excluding OTTI	(1)	0
Other-Than-Temporary Impairment on Held-to-Maturity Securities | Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Other-than-temporary impairment on held-to-maturity securities related to factors other than credit	0	(1)
Net Unrealized Losses on Retirement Plans | Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Amortization of actuarial losses, net of related tax benefits of $3 and $3, respectively	1	5
Tax on reclassification adjustment for pension and other postretirement	(2)	(4)
Interest-rate contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Net interest revenue	$ 0	$ 1