Securities (Investment Securities) (Detail) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Investment Holdings
Available-for-sale debt securities, fair value	[1]	$ 31,819	$ 31,751
Available-for-sale debt securities, unrealized losses		(516)	(134)
Available-for-sale debt securities, unrealized gains		105	308
Available-for-sale debt securities, amortized cost		32,230	31,577
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	[2]	23	24
Trading debt securities, fair value		571	492
Equity securities, fair value		418	439
U.S. Treasury and federal agencies
Investment Holdings
Available-for-sale debt securities, fair value		96	98
Available-for-sale debt securities, unrealized losses		(2)	0
Available-for-sale debt securities, unrealized gains		0	0
Available-for-sale debt securities, amortized cost		98	98
Obligations of states and political subdivisions
Investment Holdings
Available-for-sale debt securities, fair value		44	44
Available-for-sale debt securities, unrealized losses		0	0
Available-for-sale debt securities, unrealized gains		1	1
Available-for-sale debt securities, amortized cost		43	43
Held-to-maturity securities, fair value		21	22
Held-to-maturity, unrealized losses		0	0
Held-to-maturity, unrealized gains		0	0
Held-to-maturity securities, amortized cost		21	22
Agency mortgage-backed securities | Residential mortgage backed securities
Investment Holdings
Available-for-sale debt securities, fair value		15,208	15,319	[3]
Available-for-sale debt securities, unrealized losses		(285)	(80)	[3]
Available-for-sale debt securities, unrealized gains		37	118
Available-for-sale debt securities, amortized cost		15,456	15,281
Agency mortgage-backed securities | Commercial mortgage backed securities
Investment Holdings
Available-for-sale debt securities, fair value		10,455	10,167
Available-for-sale debt securities, unrealized losses		(170)	(38)
Available-for-sale debt securities, unrealized gains		13	92
Available-for-sale debt securities, amortized cost		10,612	10,113
Non-agency mortgage-backed securities | Commercial mortgage backed securities
Investment Holdings
Available-for-sale debt securities, fair value		3,190	3,293
Available-for-sale debt securities, unrealized losses		(45)	(5)
Available-for-sale debt securities, unrealized gains		16	51
Available-for-sale debt securities, amortized cost		3,219	3,247
Asset-backed securities and other debt securities
Investment Holdings
Available-for-sale debt securities, fair value		2,214	2,218
Available-for-sale debt securities, unrealized losses		(14)	(11)
Available-for-sale debt securities, unrealized gains		38	46
Available-for-sale debt securities, amortized cost		2,190	2,183
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
Other securities
Investment Holdings
Available-for-sale debt securities, fair value		612	612
Available-for-sale debt securities, unrealized losses		0	0
Available-for-sale debt securities, unrealized gains		0	0
Available-for-sale debt securities, amortized cost		$ 612	$ 612

[1] Amortized cost of $ 32,230 and $ 31,577 at March 31, 2018 and December 31, 2017 , respectively.

[2] Fair value of $ 23 and $ 24 at March 31, 2018 and December 31, 2017 , respectively.

[3] 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.