Securities (Fair Value and Gross Unrealized Losses on Available-for-Sale Securities) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 22,126	$ 11,101
Less than 12 months Unrealized Losses	(625)	(85)
12 months or more Fair Value	5,871	1,536
12 months or more Unrealized Losses	(317)	(49)
Total Fair Value	27,997	12,637
Total Unrealized Losses	(942)	(134)
U.S. Treasury and federal agencies
Investments, Unrealized Loss Position
Less than 12 months Fair Value	95	98
Less than 12 months Unrealized Losses	(3)	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	95	98
Total Unrealized Losses	(3)	0
Agency mortgage-backed securities | Residential mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	11,073	7,337
Less than 12 months Unrealized Losses	(286)	(59)
12 months or more Fair Value	3,559	479
12 months or more Unrealized Losses	(203)	(21)
Total Fair Value	14,632	7,816
Total Unrealized Losses	(489)	(80)	[1]
Agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	7,820	2,900
Less than 12 months Unrealized Losses	(269)	(22)
12 months or more Fair Value	1,701	526
12 months or more Unrealized Losses	(94)	(16)
Total Fair Value	9,521	3,426
Total Unrealized Losses	(363)	(38)
Non-agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	2,511	449
Less than 12 months Unrealized Losses	(63)	(2)
12 months or more Fair Value	214	145
12 months or more Unrealized Losses	(13)	(3)
Total Fair Value	2,725	594
Total Unrealized Losses	(76)	(5)
Asset-backed securities and other debt securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	627	317
Less than 12 months Unrealized Losses	(4)	(2)
12 months or more Fair Value	397	386
12 months or more Unrealized Losses	(7)	(9)
Total Fair Value	1,024	703
Total Unrealized Losses	$ (11)	$ (11)

[1] Includes interest-only mortgage-backed securities of $ 34 as of December 31, 2017 , recorded at fair value with fair value changes recorded in securities (losses) gains, net, in the Condensed Consolidated Statements of Income.