Stockholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Class of Stock [Line Items]
Net interest revenue	$ 513	$ 570	$ 1,594	$ 1,686
Total reclassifications out of AOCI	543	542	1,313	1,500
Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Total reclassifications out of AOCI	4	3	17	13
Net Unrealized Gains (Losses) on Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income
Class of Stock [Line Items]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax	0	0	1	1
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	(1)	0	(3)	(9)
Gain (Loss) on Investments, Excluding OTTI, Tax	0	0	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			(1)	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	4	2	19	19
OCI reclassification adjustment, pension and other postretirement benefit plans, tax	(3)	3	(4)	(2)
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	$ 1	$ 1	$ 2	$ 2