Fair Value Measurements (Assets Measured at Fair Value on a Non-recurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	$ 2,187		$ 2,187		$ 1,407
Net gain (loss) on loan sales	83	$ 55	174	$ 100
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value losses on repossessed assets	0	2	1	2
Net gain (loss) on loan sales	1	(2)	1	(3)
Nonrecurring | Provision for loan losses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value losses on loans	21	$ 17	56	$ 27
Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Repossessed assets	18		18		19
Total assets at fair value	60		60		93
Residential first mortgage loans | Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans held-for-investment	$ 42		$ 42		$ 74