Fair Value Disclosures - Roll Forward of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Non-agency MBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ 507	$ 626	$ 745
Included in earnings	[1]	36	25	23
Included in unrealized net holding gains (losses) in OCI		(40)	(45)	(45)
Purchases		0	0	0
Issuances		0	0	0
Sales		0	0	0
Settlements		(71)	(99)	(97)
Transfers into Level 3		0	0	0
Transfers out of Level 3		0	0	0
Adoption of fair value option for commercial MSRs			0
Balance at end of period		432	507	626
Change in unrealized gains (losses) included in earnings attributable to asset and liabilities still held at period end		35
MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		1,052	880	844
Included in earnings	[1]	48	63	10
Included in unrealized net holding gains (losses) in OCI		0	0	0
Purchases		0	0	0
Issuances		124	146	156
Sales		0	0	0
Settlements		(168)	(160)	(130)
Transfers into Level 3		0	0	0
Transfers out of Level 3		0	0	0
Adoption of fair value option for commercial MSRs			123
Balance at end of period		1,056	1,052	880
Change in unrealized gains (losses) included in earnings attributable to asset and liabilities still held at period end		48
Net Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		(13)	4	17
Included in earnings	[1]	38	97	81
Included in unrealized net holding gains (losses) in OCI		0	0	0
Purchases		0	0	1
Issuances		43	82	74
Sales		0	0	0
Settlements		(65)	(196)	(169)
Transfers into Level 3		0	0	0
Transfers out of Level 3		0	0	0
Adoption of fair value option for commercial MSRs			0
Balance at end of period		3	(13)	4
Change in unrealized gains (losses) included in earnings attributable to asset and liabilities still held at period end		3
Private Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		362	289	329
Included in earnings	[1]	58	20	49
Included in unrealized net holding gains (losses) in OCI		0	0	0
Purchases		142	106	81
Issuances		0	0	0
Sales		(119)	(4)	(132)
Settlements		(26)	(49)	(38)
Transfers into Level 3		0	0	0
Transfers out of Level 3		(13)	0	0
Adoption of fair value option for commercial MSRs			0
Balance at end of period		404	$ 362	$ 289
Change in unrealized gains (losses) included in earnings attributable to asset and liabilities still held at period end		$ 12

[1] Amounts related to non-agency MBS are included in interest income, amounts related to MSRs and net derivatives are primarily included in mortgage banking income and amounts related to private equity investments are included in other income in the Consolidated Statements of Income.