Fair Values of Assets and Liabilities - Changes in Fair Value for All Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Non-Agency Prime [Member] | Mortgage-Backed Securities Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	$ 297	$ 385	$ 318	$ 405
Net Gains (Losses) Included in Net Income	(1)		(1)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	3	(1)		(2)
Sales	0	0	0	0
Principal Payments	(19)	(21)	(37)	(40)
Settlements	0	0	0	0
End of Period Balance	280	363	280	363
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	3	(1)		(2)
Non-Agency Non-Prime [Member] | Mortgage-Backed Securities Residential [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	227	273	240	280
Net Gains (Losses) Included in Net Income	(1)		(1)
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	2		(3)
Sales	0	0	0	0
Principal Payments	(12)	(11)	(20)	(18)
Settlements	0	0	0	0
End of Period Balance	216	262	216	262
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	2		(3)
Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	9	9	9	9
Sales	0	0	0	0
Settlements	0	0	0	0
End of Period Balance	9	9	9	9
Asset-Backed Securities Other [Member] | Asset-Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	2	61	2	62
Net Gains (Losses) Included in Net Income		1		2
Net Gains (Losses) Included in Other Comprehensive Income (Loss)		(2)
Sales	0	0	0	0
Principal Payments		(2)		(6)
Settlements	0	0	0	0
End of Period Balance	2	58	2	58
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period		(2)
Mortgage Servicing Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	2,222	2,250	2,512	2,338
Net Gains (Losses) Included in Net Income	(302)	58	(700)	(181)
Purchases	5	9	14	15
Sales	0	0	0	0
Issuances	131	164	230	309
Settlements	0	0	0	0
End of Period Balance	2,056	2,481	2,056	2,481
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	(302)	58	(700)	(181)
Available-for-Sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	535	728	569	756
Net Gains (Losses) Included in Net Income	(2)	1	(2)	2
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	5	(3)	(3)	(2)
Sales	0	0	0	0
Principal Payments	(31)	(34)	(57)	(64)
Settlements	0	0	0	0
End of Period Balance	507	692	507	692
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	5	(3)	(3)	(2)
Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning of Period Balance	851	729	498	574
Net Gains (Losses) Included in Net Income	461	(72)	963	299
Net Gains (Losses) Included in Other Comprehensive Income (Loss)	0	0	0	0
Purchases	1		1
Sales	(1)	(4)	(3)	(5)
Principal Payments	0	0	0	0
Issuances	0	0	0	0
Settlements	(232)	(175)	(379)	(390)
End of Period Balance	1,080	478	1,080	478
Net Change in Unrealized Gains (Losses) Relating to Assets and Liabilities Held at End of Period	$ (344)	$ (131)	$ 630	$ (6)