Fair Value Measurement Fair Value Measurement - Schedule of Level 3 Inputs Reconciliation for Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Available-for-sale Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 455	$ 732	$ 578	$ 615
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income	65	0	82	13
Total Gains or (Losses) (Realized/Unrealized), Included in OCI	(37)	11	(19)	19
Purchases	50	135	110	388
Sales	(111)	0	(116)	0
Issuances	0	0	0	0
Settlements	(24)	(36)	(72)	(97)
Transfers Into Level 3	222	122	434	393
Transfers Out of Level 3	(25)	(273)	(402)	(640)
Ending balance	595	691	595	691
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held	5	8	17	22
RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	429	555	518	504
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income	65	9	82	22
Total Gains or (Losses) (Realized/Unrealized), Included in OCI	(37)	11	(19)	17
Purchases	0	51	0	110
Sales	(111)	0	(116)	0
Issuances	0	0	0	0
Settlements	(23)	(27)	(69)	(75)
Transfers Into Level 3	222	122	434	329
Transfers Out of Level 3	(25)	(137)	(310)	(323)
Ending balance	520	584	520	584
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held	5	8	17	22
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	17	128	51	97
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income	0	0	0	0
Total Gains or (Losses) (Realized/Unrealized), Included in OCI	0	0	0	2
Purchases	50	78	110	234
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(1)	(2)	(3)	(12)
Transfers Into Level 3	0	0	0	64
Transfers Out of Level 3	0	(106)	(92)	(287)
Ending balance	66	98	66	98
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held	0	0	0	0
Other ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		30		0
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income		0		0
Total Gains or (Losses) (Realized/Unrealized), Included in OCI		0		0
Purchases		0		30
Sales		0		0
Issuances		0		0
Settlements		0		0
Transfers Into Level 3		0		0
Transfers Out of Level 3		(30)		(30)
Ending balance		0		0
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held		0		0
Other securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	9	19	9	14
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income	0	(9)	0	(9)
Total Gains or (Losses) (Realized/Unrealized), Included in OCI	0	0	0	0
Purchases		6		14
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	(7)	0	(10)
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Ending balance	9	9	9	9
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held	0	0	0	0
Consumer MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	85	53	80	68
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income	1	3	(3)	(17)
Total Gains or (Losses) (Realized/Unrealized), Included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	6	7	18	15
Settlements	(2)	(1)	(5)	(4)
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Ending balance	90	62	90	62
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held	1	3	(3)	(17)
Derivative Financial Instruments, Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	57	85	47	57
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income	(2)	0	1	28
Total Gains or (Losses) (Realized/Unrealized), Included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	25	18	65	60
Settlements	(20)	(27)	(45)	(53)
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	(3)	(2)	(11)	(18)
Ending balance	57	74	57	74
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held	(2)	0	1	28
Retained interest in securitizations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	188	203	201	211
Total Gains or (Losses) (Realized/Unrealized), Included in Net Income	(10)	2	(23)	(6)
Total Gains or (Losses) (Realized/Unrealized), Included in OCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers Into Level 3	0	0	0	0
Transfers Out of Level 3	0	0	0	0
Ending balance	178	205	178	205
Net Unrealized Gains (Losses) Included in Net Income Related to Assets and Liabilities Still Held	$ (10)	$ 2	$ (23)	$ (6)