Allowance for Credit Losses - Summary of Changes in Allowance for Credit Losses and Related Loan Balance by Product (Detail) (USD $)	3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended						3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Commercial Loans [Member]	Dec. 31, 2011 Commercial Loans [Member]	Sep. 30, 2012 Commercial Loans [Member] Construction and Other Real Estate [Member]	Sep. 30, 2011 Commercial Loans [Member] Construction and Other Real Estate [Member]	Sep. 30, 2012 Commercial Loans [Member] Construction and Other Real Estate [Member]	Sep. 30, 2011 Commercial Loans [Member] Construction and Other Real Estate [Member]	Dec. 31, 2011 Commercial Loans [Member] Construction and Other Real Estate [Member]	Sep. 30, 2012 Commercial Loans [Member] Business Banking and Middle Markets Enterprises [Member]	Sep. 30, 2011 Commercial Loans [Member] Business Banking and Middle Markets Enterprises [Member]	Sep. 30, 2012 Commercial Loans [Member] Business Banking and Middle Markets Enterprises [Member]	Sep. 30, 2011 Commercial Loans [Member] Business Banking and Middle Markets Enterprises [Member]	Dec. 31, 2011 Commercial Loans [Member] Business Banking and Middle Markets Enterprises [Member]	Sep. 30, 2012 Commercial Loans [Member] Global Banking [Member]	Sep. 30, 2011 Commercial Loans [Member] Global Banking [Member]	Sep. 30, 2012 Commercial Loans [Member] Global Banking [Member]	Sep. 30, 2011 Commercial Loans [Member] Global Banking [Member]	Dec. 31, 2011 Commercial Loans [Member] Global Banking [Member]	Sep. 30, 2011 Commercial Loans [Member] Other Commercial [Member]	Sep. 30, 2012 Commercial Loans [Member] Other Commercial [Member]	Sep. 30, 2011 Commercial Loans [Member] Other Commercial [Member]	Jun. 30, 2012 Commercial Loans [Member] Other Commercial [Member]	Dec. 31, 2011 Commercial Loans [Member] Other Commercial [Member]	Sep. 30, 2012 Consumer Loans [Member]	Dec. 31, 2011 Consumer Loans [Member]	Sep. 30, 2012 Consumer Loans [Member] Residential Mortgage [Member]	Sep. 30, 2011 Consumer Loans [Member] Residential Mortgage [Member]	Sep. 30, 2012 Consumer Loans [Member] Residential Mortgage [Member]	Sep. 30, 2011 Consumer Loans [Member] Residential Mortgage [Member]	Dec. 31, 2011 Consumer Loans [Member] Residential Mortgage [Member]	Sep. 30, 2012 Consumer Loans [Member] Home Equity Mortgages [Member]	Sep. 30, 2011 Consumer Loans [Member] Home Equity Mortgages [Member]	Sep. 30, 2012 Consumer Loans [Member] Home Equity Mortgages [Member]	Sep. 30, 2011 Consumer Loans [Member] Home Equity Mortgages [Member]	Dec. 31, 2011 Consumer Loans [Member] Home Equity Mortgages [Member]	Sep. 30, 2012 Consumer Loans [Member] Credit Card Receivables [Member]	Sep. 30, 2011 Consumer Loans [Member] Credit Card Receivables [Member]	Sep. 30, 2012 Consumer Loans [Member] Credit Card Receivables [Member]	Sep. 30, 2011 Consumer Loans [Member] Credit Card Receivables [Member]	Dec. 31, 2011 Consumer Loans [Member] Credit Card Receivables [Member]	Sep. 30, 2012 Consumer Loans [Member] Other Consumer [Member]	Sep. 30, 2011 Consumer Loans [Member] Other Consumer [Member]	Sep. 30, 2012 Consumer Loans [Member] Other Consumer [Member]	Sep. 30, 2011 Consumer Loans [Member] Other Consumer [Member]	Dec. 31, 2011 Consumer Loans [Member] Other Consumer [Member]
Balance at beginning of period	$ 619,000,000	$ 747,000,000	$ 743,000,000	$ 852,000,000				$ 198,000,000	$ 229,000,000	$ 212,000,000	$ 243,000,000		$ 80,000,000	$ 96,000,000	$ 78,000,000	$ 132,000,000		$ 44,000,000	$ 110,000,000	$ 131,000,000	$ 116,000,000		$ 21,000,000	$ 21,000,000	$ 32,000,000	$ 18,000,000				$ 188,000,000	$ 162,000,000	$ 192,000,000	$ 167,000,000		$ 47,000,000	$ 62,000,000	$ 52,000,000	$ 77,000,000		$ 31,000,000	$ 44,000,000	$ 39,000,000	$ 58,000,000		$ 13,000,000	$ 23,000,000	$ 18,000,000	$ 27,000,000
Provision charged to income	84,000,000	78,000,000	173,000,000	171,000,000				(11,000,000)	(10,000,000)	(36,000,000)	11,000,000		18,000,000	5,000,000	39,000,000	(4,000,000)		12,000,000	28,000,000	9,000,000	22,000,000		(23,000,000)	(9,000,000)	(33,000,000)					33,000,000	53,000,000	72,000,000	98,000,000		13,000,000	8,000,000	55,000,000	31,000,000		15,000,000	12,000,000	35,000,000	32,000,000		4,000,000	5,000,000	8,000,000	14,000,000
Charge offs	(76,000,000)	(75,000,000)	(329,000,000)	(300,000,000)				(9,000,000)	(3,000,000)	(12,000,000)	(46,000,000)		(8,000,000)	(11,000,000)	(31,000,000)	(44,000,000)				(84,000,000)					(2,000,000)					(24,000,000)	(24,000,000)	(73,000,000)	(78,000,000)		(18,000,000)	(15,000,000)	(65,000,000)	(53,000,000)		(14,000,000)	(16,000,000)	(47,000,000)	(56,000,000)		(3,000,000)	(6,000,000)	(17,000,000)	(21,000,000)
Recoveries	10,000,000	29,000,000	50,000,000	56,000,000				3,000,000	1,000,000	17,000,000	9,000,000		2,000,000	3,000,000	6,000,000	9,000,000							20,000,000	6,000,000	21,000,000					3,000,000	1,000,000	9,000,000	4,000,000							2,000,000	3,000,000	7,000,000	9,000,000			1,000,000	5,000,000	4,000,000
Net charge offs	(66,000,000)	(46,000,000)	(279,000,000)	(244,000,000)				(6,000,000)	(2,000,000)	5,000,000	(37,000,000)		(6,000,000)	(8,000,000)	(25,000,000)	(35,000,000)				(84,000,000)			20,000,000	6,000,000	19,000,000					(21,000,000)	(23,000,000)	(64,000,000)	(74,000,000)		(18,000,000)	(15,000,000)	(65,000,000)	(53,000,000)		(12,000,000)	(13,000,000)	(40,000,000)	(47,000,000)		(3,000,000)	(5,000,000)	(12,000,000)	(17,000,000)
Allowance on loans transferred to held for sale		(30,000,000)		(30,000,000)										(10,000,000)		(10,000,000)															(4,000,000)		(3,000,000)			(6,000,000)		(6,000,000)			(6,000,000)		(6,000,000)			(4,000,000)		(5,000,000)
Balance at end of period	637,000,000	749,000,000	637,000,000	749,000,000				181,000,000	217,000,000	181,000,000	217,000,000		92,000,000	83,000,000	92,000,000	83,000,000		56,000,000	138,000,000	56,000,000	138,000,000		18,000,000	18,000,000	18,000,000	18,000,000				200,000,000	188,000,000	200,000,000	188,000,000		42,000,000	49,000,000	42,000,000	49,000,000		34,000,000	37,000,000	34,000,000	37,000,000		14,000,000	19,000,000	14,000,000	19,000,000
Ending balance: collectively evaluated for impairment	391,000,000	423,000,000	391,000,000	423,000,000				79,000,000	114,000,000	79,000,000	114,000,000		82,000,000	68,000,000	82,000,000	68,000,000		41,000,000	31,000,000	41,000,000	31,000,000		14,000,000	17,000,000	14,000,000					93,000,000	102,000,000	93,000,000	102,000,000		36,000,000	45,000,000	36,000,000	45,000,000		29,000,000	30,000,000	29,000,000	30,000,000		14,000,000	19,000,000	14,000,000	19,000,000
Ending balance: individually evaluated for impairment	246,000,000	326,000,000	246,000,000	326,000,000				102,000,000	103,000,000	102,000,000	103,000,000		10,000,000	15,000,000	10,000,000	15,000,000		15,000,000	107,000,000	15,000,000	107,000,000		4,000,000	1,000,000	4,000,000					107,000,000	86,000,000	107,000,000	86,000,000		6,000,000	4,000,000	6,000,000	4,000,000		5,000,000	7,000,000	5,000,000	7,000,000
Total allowances for credit losses	637,000,000	749,000,000	637,000,000	749,000,000				181,000,000	217,000,000	181,000,000	217,000,000		92,000,000	83,000,000	92,000,000	83,000,000		56,000,000	138,000,000	56,000,000	138,000,000		18,000,000	18,000,000	18,000,000	18,000,000				200,000,000	188,000,000	200,000,000	188,000,000		42,000,000	49,000,000	42,000,000	49,000,000		34,000,000	37,000,000	34,000,000	37,000,000		14,000,000	19,000,000	14,000,000	19,000,000
Collectively evaluated for impairment	58,920,000,000	47,222,000,000	58,920,000,000	47,222,000,000				7,387,000,000	7,066,000,000	7,387,000,000	7,066,000,000		12,389,000	9,842,000,000	12,389,000	9,842,000,000		18,868,000,000	11,908,000,000	18,868,000,000	11,908,000,000		1,650,000,000	3,054,000,000	1,650,000,000					13,462,000,000	12,653,000,000	13,462,000,000	12,653,000,000		2,365,000,000	2,604,000,000	2,365,000,000	2,604,000,000		780,000,000	766,000,000	780,000,000	766,000,000		615,000,000	733,000,000	615,000,000	733,000,000
Individually evaluated for impairment	1,253,000,000	1,326,000,000	1,253,000,000	1,326,000,000				533,000,000	707,000,000	533,000,000	707,000,000		108,000,000	155,000,000	108,000,000	155,000,000		143,000,000	147,000,000	143,000,000	147,000,000		144,000,000	86,000,000	144,000,000					345,000,000	137,000,000	345,000,000	137,000,000		22,000,000	14,000,000	22,000,000	14,000,000		16,000,000	22,000,000	16,000,000	22,000,000
Loans carried at the lower of amortized cost or fair value less cost to sell	1,279,000,000	1,052,000,000	1,279,000,000	1,052,000,000																										1,279,000,000	1,052,000,000	1,279,000,000	1,052,000,000
Total	$ 61,452,000,000	$ 49,600,000,000	$ 61,452,000,000	$ 49,600,000,000	$ 51,867,000,000	$ 42,568,000,000	$ 33,649,000,000	$ 7,920,000,000	$ 7,773,000,000	$ 7,920,000,000	$ 7,773,000,000	$ 7,860,000,000	$ 12,497,000,000	$ 9,997,000,000	$ 12,497,000,000	$ 9,997,000,000	$ 10,225,000,000	$ 19,011,000,000	$ 12,055,000,000	$ 19,011,000,000	$ 12,055,000,000	$ 12,658,000,000	$ 1,794,000,000	$ 3,140,000,000	$ 1,794,000,000		$ 2,906,000,000	$ 18,884,000,000	$ 18,218,000,000	$ 15,086,000,000	$ 13,842,000,000	$ 15,086,000,000	$ 13,842,000,000	$ 14,113,000,000	$ 2,387,000,000	$ 2,618,000,000	$ 2,387,000,000	$ 2,618,000,000	$ 2,563,000,000	$ 796,000,000	$ 788,000,000	$ 796,000,000	$ 788,000,000	$ 828,000,000	$ 615,000,000	$ 733,000,000	$ 615,000,000	$ 733,000,000	$ 714,000,000