Securities (Fair Value and Gross Unrealized Losses on Available-for-Sale Securities) (Detail) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 22,669	$ 11,101
Less than 12 months Unrealized Losses	(443)	(85)
12 months or more Fair Value	1,488	1,536
12 months or more Unrealized Losses	(73)	(49)
Total Fair Value	24,157	12,637
Total Unrealized Losses	(516)	(134)
U.S. Treasury and federal agencies
Investments, Unrealized Loss Position
Less than 12 months Fair Value	96	98
Less than 12 months Unrealized Losses	(2)	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	96	98
Total Unrealized Losses	(2)	0
Agency mortgage-backed securities | Residential mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	11,958	7,337
Less than 12 months Unrealized Losses	(256)	(59)
12 months or more Fair Value	458	479
12 months or more Unrealized Losses	(29)	(21)
Total Fair Value	12,416	7,816
Total Unrealized Losses	(285)	(80)	[1]
Agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	8,115	2,900
Less than 12 months Unrealized Losses	(144)	(22)
12 months or more Fair Value	512	526
12 months or more Unrealized Losses	(26)	(16)
Total Fair Value	8,627	3,426
Total Unrealized Losses	(170)	(38)
Non-agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	2,188	449
Less than 12 months Unrealized Losses	(38)	(2)
12 months or more Fair Value	141	145
12 months or more Unrealized Losses	(7)	(3)
Total Fair Value	2,329	594
Total Unrealized Losses	(45)	(5)
Asset-backed securities and other debt securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	312	317
Less than 12 months Unrealized Losses	(3)	(2)
12 months or more Fair Value	377	386
12 months or more Unrealized Losses	(11)	(9)
Total Fair Value	689	703
Total Unrealized Losses	$ (14)	$ (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 gains, net, in the Condensed Consolidated Statements of Income.