Fair Value and Gross Unrealized Losses on Available-for-Sale Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2015		Dec. 31, 2014
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 2,076		$ 714
Less than 12 months Unrealized Losses	(16)		(3)
12 months or more Fair Value	194		104
12 months or more Unrealized Losses	(6)		(2)
Total Fair Value	2,270		818
Total Unrealized Losses	(22)		(5)
Agency mortgage-backed securities | Residential mortgage backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	1,321		73
Less than 12 months Unrealized Losses	(4)		(1)
Total Fair Value	1,321		73
Total Unrealized Losses	(4)	[1]	(1)	[2]
Agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value			355
Less than 12 months Unrealized Losses			(1)
Total Fair Value			355
Total Unrealized Losses			(1)
Non-agency mortgage-backed securities | Commercial mortgage backed securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	497
Less than 12 months Unrealized Losses	(7)
Total Fair Value	497
Total Unrealized Losses	(7)
Asset-backed securities and other debt securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	258		286
Less than 12 months Unrealized Losses	(5)		(1)
12 months or more Fair Value	164		74
12 months or more Unrealized Losses	(5)		(1)
Total Fair Value	422		360
Total Unrealized Losses	(10)		(2)
Equity securities
Investments, Unrealized Loss Position [Line Items]
12 months or more Fair Value	30		30
12 months or more Unrealized Losses	(1)		(1)
Total Fair Value	30		30
Total Unrealized Losses	$ (1)	[3]	$ (1)	[4]

[1] 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.

[2] 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.

[3] 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.

[4] 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