Securities (Available-for-Sale and Held-to-Maturity Securities) (Detail) - USD ($) $ in Millions		Sep. 30, 2017		Dec. 31, 2016
Investment Holdings
Available-for-sale securities, fair value	[1]	$ 31,480		$ 31,183
Available-for-sale securities, unrealized losses		(89)		(191)
Available-for-sale securities, unrealized gains		455		350
Available-for-sale and other securities, Amortized Cost		31,114		31,024
Held-to-maturity securities, fair value		25		26
Held-to-maturity, unrealized losses		0		0
Held-to-maturity, unrealized gains		0		0
Held-to-maturity securities, amortized cost	[2]	25		26
U.S. Treasury and federal agencies
Investment Holdings
Available-for-sale securities, fair value		69		549
Available-for-sale securities, unrealized losses		0		0
Available-for-sale securities, unrealized gains		0		2
Available-for-sale and other securities, Amortized Cost		69		547
Obligations of states and political subdivisions
Investment Holdings
Available-for-sale securities, fair value		45		45
Available-for-sale securities, unrealized losses		0		0
Available-for-sale securities, unrealized gains		1		1
Available-for-sale and other securities, Amortized Cost		44		44
Held-to-maturity securities, fair value		23		24
Held-to-maturity, unrealized losses		0		0
Held-to-maturity, unrealized gains		0		0
Held-to-maturity securities, amortized cost		23		24
Agency mortgage-backed securities | Residential mortgage backed securities
Investment Holdings
Available-for-sale securities, fair value		15,933	[3]	15,608	[4]
Available-for-sale securities, unrealized losses		(35)	[3]	(95)	[4]
Available-for-sale securities, unrealized gains		218	[3]	178	[4]
Available-for-sale and other securities, Amortized Cost		15,750	[3]	15,525	[4]
Agency mortgage-backed securities | Commercial mortgage backed securities
Investment Holdings
Available-for-sale securities, fair value		9,232		9,055
Available-for-sale securities, unrealized losses		(35)		(61)
Available-for-sale securities, unrealized gains		130		87
Available-for-sale and other securities, Amortized Cost		9,137		9,029
Non-agency mortgage-backed securities | Commercial mortgage backed securities
Investment Holdings
Available-for-sale securities, fair value		3,358		3,112
Available-for-sale securities, unrealized losses		(4)		(15)
Available-for-sale securities, unrealized gains		62		51
Available-for-sale and other securities, Amortized Cost		3,300		3,076
Asset-backed securities and other debt securities
Investment Holdings
Available-for-sale securities, fair value		2,143		2,116
Available-for-sale securities, unrealized losses		(14)		(18)
Available-for-sale securities, unrealized gains		41		28
Available-for-sale and other securities, Amortized Cost		2,116		2,106
Held-to-maturity securities, fair value		2		2
Held-to-maturity, unrealized losses		0		0
Held-to-maturity, unrealized gains		0		0
Held-to-maturity securities, amortized cost		2		2
Equity securities
Investment Holdings
Available-for-sale securities, fair value		700	[5]	698	[6]
Available-for-sale securities, unrealized losses		(1)	[5]	(2)	[6]
Available-for-sale securities, unrealized gains		3	[5]	3	[6]
Available-for-sale and other securities, Amortized Cost		$ 698	[5]	$ 697	[6]

[1] Amortized cost of $ 31,114 and $ 31,024 at September 30, 2017 and December 31, 2016 , respectively.

[2] Fair value of $ 25 and $ 26 at September 30, 2017 and December 31, 2016 , respectively.

[3] 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.

[4] 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.

[5] 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.

[6] 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