Available-for-Sale and Held-to-Maturity Securities (Detail) - USD ($) $ in Millions		Sep. 30, 2015		Dec. 31, 2014
Investment Holdings [Line Items]
Available-for-sale securities, fair value	[1]	$ 28,799		$ 22,408
Available-for-sale securities, unrealized losses		(22)		(5)
Available-for-sale securities, unrealized gains		835		736
Available-for-sale and other securities, Amortized Cost		27,986		21,677
Held-to-maturity securities, fair value		157		187
Held-to-maturity securities, amortized cost	[2]	157		187
U.S. Treasury and federal agencies
Investment Holdings [Line Items]
Available-for-sale securities, fair value		1,123		1,632
Available-for-sale securities, unrealized gains		46		87
Available-for-sale and other securities, Amortized Cost		1,077		1,545
Obligations of states and political subdivisions
Investment Holdings [Line Items]
Available-for-sale securities, fair value		142		192
Available-for-sale securities, unrealized gains		5		7
Available-for-sale and other securities, Amortized Cost		137		185
Held-to-maturity securities, fair value		155		186
Held-to-maturity securities, amortized cost		155		186
Agency mortgage-backed securities | Residential mortgage backed securities
Investment Holdings [Line Items]
Available-for-sale securities, fair value		14,879	[3]	12,404	[4]
Available-for-sale securities, unrealized losses		(4)	[3]	(1)	[4]
Available-for-sale securities, unrealized gains		460	[3]	437	[4]
Available-for-sale and other securities, Amortized Cost		14,423	[3]	11,968	[4]
Agency mortgage-backed securities | Commercial mortgage backed securities
Investment Holdings [Line Items]
Available-for-sale securities, fair value		7,838		4,565
Available-for-sale securities, unrealized losses				(1)
Available-for-sale securities, unrealized gains		229		101
Available-for-sale and other securities, Amortized Cost		7,609		4,465
Non-agency mortgage-backed securities | Commercial mortgage backed securities
Investment Holdings [Line Items]
Available-for-sale securities, fair value		2,757		1,550
Available-for-sale securities, unrealized losses		(7)
Available-for-sale securities, unrealized gains		71		61
Available-for-sale and other securities, Amortized Cost		2,693		1,489
Asset-backed securities and other debt securities
Investment Holdings [Line Items]
Available-for-sale securities, fair value		1,356		1,362
Available-for-sale securities, unrealized losses		(10)		(2)
Available-for-sale securities, unrealized gains		21		40
Available-for-sale and other securities, Amortized Cost		1,345		1,324
Held-to-maturity securities, fair value		2		1
Held-to-maturity securities, amortized cost		2		1
Equity securities
Investment Holdings [Line Items]
Available-for-sale securities, fair value		704	[5]	703	[6]
Available-for-sale securities, unrealized losses		(1)	[5]	(1)	[6]
Available-for-sale securities, unrealized gains		3	[5]	3	[6]
Available-for-sale and other securities, Amortized Cost		$ 702	[5]	$ 701	[6]

[1] Amortized cost of $27,986 and $21,677 at September 30, 2015 and December 31, 2014, respectively.

[2] Fair value of $157 and $187 at September 30, 2015 and December 31, 2014, respectively.

[3] Includes interest-only mortgage-backed securities of $53 as of September 30, 2015 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 $175 as of December 31, 2014, 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 and FRB restricted stock holdings of $248 and $354, respectively, at September 30, 2015, that are carried at cost, and certain mutual fund and equity security holdings.

[6] Equity securities consist of FHLB and FRB restricted stock holdings of $248 and $352, respectively, at December 31, 2014, that are carried at cost, and certain mutual fund and equity security holdings