Securities - Amortized Cost and Fair Value of Asset Backed Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Sep. 30, 2014	Dec. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		$ 29,654	[1]	$ 54,935	[1]
Unrealized Gains, Available-for-sale securities		621		698
Unrealized Losses, Available-for-sale securities		(135)		(727)
Fair Value, Available-for-sale securities		30,140		54,906
Amortized Cost, Held-to-Maturity Securities		13,469	[1]	1,462	[1]
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities				(104)
Unrealized Gains, Held-to-maturity securities		229		141
Unrealized Losses, Held-to-maturity securities		(3)		0
Held-to-maturity Securities, Fair Value		13,695		1,499
Available-for-sale Securities, Transfers to Held-to-maturity Securities, Fair Value	10,985
Accumulated Other Comprehensive Income (Loss), Net Unrealized Gains (Losses) on Transfers from Available-for-Sale to Held-to Maturity Securities, Before Tax	(234)
U.S. Treasury [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		11,793	[1]	27,716	[1]
Unrealized Gains, Available-for-sale securities		276		391
Unrealized Losses, Available-for-sale securities		(58)		(113)
Fair Value, Available-for-sale securities		12,011		27,994
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		520	[1],[2]	159	[1],[2]
Unrealized Gains, Available-for-sale securities		5	[2]	0	[2]
Unrealized Losses, Available-for-sale securities		(1)	[2]	(14)	[2]
Fair Value, Available-for-sale securities		524	[2]	145	[2]
Amortized Cost, Held-to-Maturity Securities		4,868	[1],[3]	845	[1],[3]
Unrealized Gains, Held-to-maturity securities		120	[3]	88	[3]
Unrealized Losses, Held-to-maturity securities		(1)	[3]	0	[3]
Held-to-maturity Securities, Fair Value		4,987	[3]	933	[3]
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		35	[1],[2]	41	[1],[2]
Unrealized Gains, Available-for-sale securities		0	[2]	0	[2]
Unrealized Losses, Available-for-sale securities		0	[2]	(1)	[2]
Fair Value, Available-for-sale securities		35	[2]	40	[2]
Direct agency obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		3,995	[1],[2]	4,115	[1],[2]
Unrealized Gains, Available-for-sale securities		217	[2]	225	[2]
Unrealized Losses, Available-for-sale securities		(6)	[2]	(16)	[2]
Fair Value, Available-for-sale securities		4,206	[2]	4,324	[2]
Mortgage-backed securities, issued or guaranteed by US Government agency [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		7,985	[1]	10,304	[1]
Unrealized Gains, Available-for-sale securities		101		40
Unrealized Losses, Available-for-sale securities		(27)		(342)
Fair Value, Available-for-sale securities		8,059		10,002
Amortized Cost, Held-to-Maturity Securities		3,700	[1]	52	[1]
Unrealized Gains, Held-to-maturity securities		53		8
Unrealized Losses, Held-to-maturity securities		(1)		0
Held-to-maturity Securities, Fair Value		3,752		60
Collateralized mortgage obligations, issued or guaranteed by US Government agency [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		329	[1]	6,584	[1]
Unrealized Gains, Available-for-sale securities		3		17
Unrealized Losses, Available-for-sale securities		(2)		(154)
Fair Value, Available-for-sale securities		330		6,447
Amortized Cost, Held-to-Maturity Securities		4,867	[1]	214	[1]
Unrealized Gains, Held-to-maturity securities		54		24
Unrealized Losses, Held-to-maturity securities		(1)		0
Held-to-maturity Securities, Fair Value		4,920		238
Obligations of U.S. states and political subdivision [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		661	[1]	755	[1]
Unrealized Gains, Available-for-sale securities		10		12
Unrealized Losses, Available-for-sale securities		(4)		(25)
Fair Value, Available-for-sale securities		667		742
Amortized Cost, Held-to-Maturity Securities		23	[1]	29	[1]
Unrealized Gains, Held-to-maturity securities		1		1
Unrealized Losses, Held-to-maturity securities		0		0
Held-to-maturity Securities, Fair Value		24		30
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities				1	[1]
Unrealized Gains, Available-for-sale securities				0
Unrealized Losses, Available-for-sale securities				0
Fair Value, Available-for-sale securities				1
Amortized Cost, Held-to-Maturity Securities		11	[1]	18	[1]
Unrealized Gains, Held-to-maturity securities		1		1
Unrealized Losses, Held-to-maturity securities		0		0
Held-to-maturity Securities, Fair Value		12		19
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		43	[1]	125	[1]
Unrealized Gains, Available-for-sale securities		0		1
Unrealized Losses, Available-for-sale securities		0		0
Fair Value, Available-for-sale securities		43		126
Home Equity Backed Securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		97	[1]	263	[1]
Unrealized Gains, Available-for-sale securities		0		0
Unrealized Losses, Available-for-sale securities		(8)		(36)
Fair Value, Available-for-sale securities		89		227
Other securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		110	[1]	100	[1]
Unrealized Gains, Available-for-sale securities		0		0
Unrealized Losses, Available-for-sale securities		(16)		(6)
Fair Value, Available-for-sale securities		94		94
Foreign debt securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		3,921	[1],[4]	4,607	[1],[4]
Unrealized Gains, Available-for-sale securities		6	[4]	10	[4]
Unrealized Losses, Available-for-sale securities		(12)	[4]	(15)	[4]
Fair Value, Available-for-sale securities		3,915	[4]	4,602	[4]
Foreign debt securities [Member] | Foreign Government [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		689		1,101
Equity securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		165	[1]	165	[1]
Unrealized Gains, Available-for-sale securities		3		2
Unrealized Losses, Available-for-sale securities		(1)		(5)
Fair Value, Available-for-sale securities		167		162
Asset-backed securities and other debt securities held by a consolidated VIE [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Held-to-Maturity Securities				304	[1],[5]
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities				(104)	[5]
Unrealized Gains, Held-to-maturity securities				19	[5]
Unrealized Losses, Held-to-maturity securities				0	[5]
Held-to-maturity Securities, Fair Value				219	[5]
US Government sponsored enterprises [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		521		167
Amortized Cost, Held-to-Maturity Securities		3,185		398
US Government sponsored enterprises [Member] | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities		34		33
Amortized Cost, Held-to-Maturity Securities		$ 1,683		$ 447

[1] During the third quarter of 2014, we transferred U.S. government sponsored and U.S. government agency mortgage-backed securities with a fair value of $10,985 million from available-for-sale to held-to-maturity. These securities were transferred to held-to-maturity at fair value as of the transfer date with the fair value amount becoming the amortized cost basis for the transferred securities. The difference between the par value of the securities and their fair value at the date of transfer will be amortized as an adjustment to yield over the remaining contractual life of each security. At the date of the transfer, AOCI included net pretax unrealized losses of $234 million related to the transferred securities which will be amortized over the remaining contractual life of each security as an adjustment of yield in a manner consistent with the amortization of any premium or discount. The transfers reflect our intent to hold the securities to maturity and will reduce the impact of price volatility on AOCI and regulatory capital under Basel III.

[2] Includes securities at amortized cost of $521 million and $167 million issued or guaranteed by FNMA at December 31, 2014 and 2013, respectively, and $34 million and $33 million issued or guaranteed by FHLMC at December 31, 2014 and 2013, respectively.

[3] Includes securities at amortized cost of $3,185 million and $398 million issued or guaranteed by FNMA at December 31, 2014 and 2013, respectively, and $1,683 million and $447 million issued and guaranteed by FHLMC at December 31, 2014 and 2013, respectively.

[4] At December 31, 2014 and 2013, foreign debt securities consisted of $689 million and $1,101 million, respectively, of securities fully backed by foreign governments. The remainder of foreign debt securities represents public sector entity, bank or corporate debt.

[5] Relates to securities held by Bryant Park Funding LLC ("Bryant Park"), a variable interest entity which was consolidated in 2013. During the fourth quarter of 2014, the securities underlying Bryant Park were sold and the related agreements were terminated. See Note 25, "Variable Interest Entities" for additional information.