Stockholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Net interest revenue	$ (2,088)	$ (2,260)	$ (2,303)
Total reclassifications out of AOCI	(1,848)	(1,958)	$ (2,016)
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Total reclassifications out of AOCI	77	(74)
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	2	2
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	(6)	(9)
Tax on investments, excluding OTTI	1	(6)
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	(2)	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	88	(69)
Tax on reclassification adjustment for pension and other postretirement	(51)	(50)
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	$ (3)	$ 3