Securities (Fair Value and Gross Unrealized Losses on Available-for-Sale Securities) (Detail) - USD ($) $ in Millions	Sep. 30, 2017		Dec. 31, 2016
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 5,377		$ 11,079
Less than 12 months Unrealized Losses	(52)		(172)
12 months or more Fair Value	1,183		545
12 months or more Unrealized Losses	(37)		(19)
Total Fair Value	6,560		11,624
Total Unrealized Losses	(89)		(191)
U.S. Treasury and federal agencies
Investments, Unrealized Loss Position
Less than 12 months Fair Value			199
Less than 12 months Unrealized Losses			0
12 months or more Fair Value			0
12 months or more Unrealized Losses			0
Total Fair Value			199
Total Unrealized Losses	0		0
Agency mortgage-backed securities | Residential mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	2,527		6,223
Less than 12 months Unrealized Losses	(16)		(88)
12 months or more Fair Value	598		172
12 months or more Unrealized Losses	(19)		(7)
Total Fair Value	3,125		6,395
Total Unrealized Losses	(35)	[1]	(95)	[2]
Agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	2,266		3,183
Less than 12 months Unrealized Losses	(30)		(61)
12 months or more Fair Value	135		0
12 months or more Unrealized Losses	(5)		0
Total Fair Value	2,401		3,183
Total Unrealized Losses	(35)		(61)
Non-agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	403		1,052
Less than 12 months Unrealized Losses	(4)		(15)
12 months or more Fair Value	6		0
12 months or more Unrealized Losses	0		0
Total Fair Value	409		1,052
Total Unrealized Losses	(4)		(15)
Asset-backed securities and other debt securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	181		422
Less than 12 months Unrealized Losses	(2)		(8)
12 months or more Fair Value	407		336
12 months or more Unrealized Losses	(12)		(10)
Total Fair Value	588		758
Total Unrealized Losses	(14)		(18)
Equity securities
Investments, Unrealized Loss Position
Less than 12 months Fair Value	0		0
Less than 12 months Unrealized Losses	0		0
12 months or more Fair Value	37		37
12 months or more Unrealized Losses	(1)		(2)
Total Fair Value	37		37
Total Unrealized Losses	$ (1)	[3]	$ (2)	[4]

[1] Includes interest-only mortgage-backed securities of $ 36 as of September 30, 2017 , recorded at fair value with fair value changes recorded in securities gains, net, in the Condensed Consolidated Statements of Income.

[2] Includes interest-only mortgage-backed securities of $ 60 as of December 31, 2016 , recorded at fair value with fair value changes recorded in securities gains, net, in the Condensed Consolidated Statements of Income.

[3] Equity securities consist of FHLB, FRB and DTCC restricted stock holdings of $ 248 , $ 361 and $ 2 , respectively, at September 30, 2017 , that are carried at cost, and certain mutual fund and equity security holdings.

[4] Equity securities consist of FHLB, FRB and DTCC restricted stock holdings of $ 248 , $ 358 and $ 1 , respectively, at December 31, 2016 , that are carried at cost, and certain mutual fund and equity security holdings