Securities - Amortized Cost and Fair Value of Asset Backed Securities (Detail) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		$ 32,573	$ 37,502
Unrealized Gains, Available-for-sale securities		281	229
Unrealized Losses, Available-for-sale securities		(539)	(821)
Fair Value, Available-for-sale securities		32,315	36,910
Amortized Cost, Held-to-Maturity Securities		13,434	12,809
Unrealized Gains, Held-to-maturity securities		113	116
Unrealized Losses, Held-to-maturity securities		(69)	(87)
Held-to-maturity Securities, Fair Value		13,478	12,838
U.S. Treasury [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		16,871	21,366
Unrealized Gains, Available-for-sale securities		156	102
Unrealized Losses, Available-for-sale securities		(334)	(559)
Fair Value, Available-for-sale securities		16,693	20,909
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		4,023	4,535
Unrealized Gains, Available-for-sale securities		5	4
Unrealized Losses, Available-for-sale securities		(83)	(122)
Fair Value, Available-for-sale securities		3,945	4,417
Amortized Cost, Held-to-Maturity Securities		2,272	2,465
Unrealized Gains, Held-to-maturity securities		14	11
Unrealized Losses, Held-to-maturity securities		(6)	(9)
Held-to-maturity Securities, Fair Value		2,280	2,467
Collateralized Mortgage Obligations, Issued by U.S. Government Sponsored Enterprises [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		648	2,139
Unrealized Gains, Available-for-sale securities		0	0
Unrealized Losses, Available-for-sale securities		(25)	(36)
Fair Value, Available-for-sale securities		623	2,103
Amortized Cost, Held-to-Maturity Securities		1,429	1,591
Unrealized Gains, Held-to-maturity securities		53	59
Unrealized Losses, Held-to-maturity securities		(10)	(12)
Held-to-maturity Securities, Fair Value		1,472	1,638
Direct Agency Obligations U S Government Sponsored Enterprises [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		3,644	3,709
Unrealized Gains, Available-for-sale securities		106	118
Unrealized Losses, Available-for-sale securities		(2)	(10)
Fair Value, Available-for-sale securities		3,748	3,817
Mortgage-backed Securities, Issued or Guaranteed by US Government Agency [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		4,785	3,102
Unrealized Gains, Available-for-sale securities		2	2
Unrealized Losses, Available-for-sale securities		(73)	(58)
Fair Value, Available-for-sale securities		4,714	3,046
Amortized Cost, Held-to-Maturity Securities		2,318	2,557
Unrealized Gains, Held-to-maturity securities		6	11
Unrealized Losses, Held-to-maturity securities		(12)	(10)
Held-to-maturity Securities, Fair Value		2,312	2,558
Collateralized Mortgage Obligations, Issued or Guaranteed by US Government Agency [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		1,038	1,370
Unrealized Gains, Available-for-sale securities		3	2
Unrealized Losses, Available-for-sale securities		(11)	(15)
Fair Value, Available-for-sale securities		1,030	1,357
Amortized Cost, Held-to-Maturity Securities		7,396	6,176
Unrealized Gains, Held-to-maturity securities		39	34
Unrealized Losses, Held-to-maturity securities		(41)	(56)
Held-to-maturity Securities, Fair Value		7,394	6,154
Direct Agency Obligations [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		423	423
Unrealized Gains, Available-for-sale securities		9	1
Unrealized Losses, Available-for-sale securities		0	(4)
Fair Value, Available-for-sale securities		432	420
Obligations of U.S. states and political subdivision [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Held-to-Maturity Securities		14	15
Unrealized Gains, Held-to-maturity securities		1	1
Unrealized Losses, Held-to-maturity securities		0	0
Held-to-maturity Securities, Fair Value		15	16
Home Equity [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		61	69
Unrealized Gains, Available-for-sale securities		0	0
Unrealized Losses, Available-for-sale securities		(5)	(8)
Fair Value, Available-for-sale securities		56	61
Other [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		508	108
Unrealized Gains, Available-for-sale securities		0	0
Unrealized Losses, Available-for-sale securities		0	(3)
Fair Value, Available-for-sale securities		508	105
Foreign debt securities [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	[1]	413	522
Unrealized Gains, Available-for-sale securities	[1]	0	0
Unrealized Losses, Available-for-sale securities	[1]	(1)	(1)
Fair Value, Available-for-sale securities	[1]	412	521
Equity securities [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		159	159
Unrealized Gains, Available-for-sale securities		0	0
Unrealized Losses, Available-for-sale securities		(5)	(5)
Fair Value, Available-for-sale securities		154	154
Residential Mortgages [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Amortized Cost, Held-to-Maturity Securities		5	5
Unrealized Gains, Held-to-maturity securities		0	0
Unrealized Losses, Held-to-maturity securities		0	0
Held-to-maturity Securities, Fair Value		$ 5	$ 5

[1] Foreign debt securities represent public sector entity, bank or corporate debt.