Fair Value Measurements - Summary of Changes in Level 3 Fair Value Category (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	$ 13,626,233	$ 14,095,050	$ 14,019,216	$ 15,874,571
Additions of VIEs consolidated				(350,624)
Included in earnings	367,070	139,373	527,590	418,732
Included in other comprehensive income	386,830	(407,837)	558,465	42,465
Issuances
Sales				(16,600)
Settlements	(50,728)	(52,002)	(508,182)	(323,281)
Transfers in Level 3	(576,272)	(192,773)	(1,494,714)	(448,913)
Transfers out of Level 3		40,754	650,758	321,182
Deconsolidation of VIEs				(1,894,967)
Balance, end of period	13,753,133	13,662,565	13,753,133	13,662,565
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	363,599	162,300	409,121	425,901
Investments contract [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	2,162,062	2,023,513	2,199,338	1,904,361
Included in earnings	(64,826)	145,804	(127,539)	210,393
Included in other comprehensive income	62,877	(62,870)	88,314	(8,307)
Issuances
Balance, end of period	2,160,113	2,106,447	2,160,113	2,106,447
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	(64,826)	145,830	(127,539)	210,393
Loan [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	14,238,273	14,442,912	14,126,994	15,800,918
Included in earnings	439,649	126,130	738,121	481,446
Included in other comprehensive income	392,548	(389,166)	541,215	51,354
Issuances
Settlements	(85,811)	(132,909)	(421,671)	(391,784)
Deconsolidation of VIEs				(1,894,967)
Balance, end of period	14,984,659	14,046,967	14,984,659	14,046,967
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	439,649	126,156	738,602	480,391
Derivatives Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period				4,511
Included in earnings				(4,511)
Issuances
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date				(4,511)
Long-term Debt [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	(2,346,060)	(2,310,972)	(1,934,642)	(1,856,366)
Additions of VIEs consolidated				(350,624)
Included in earnings	(33,245)	166,532	(148,573)	63,605
Included in other comprehensive income	(69,066)	52,650	(77,761)	(41)
Issuances
Settlements	31,302	12,765	64,195	40,113
Transfers in Level 3	(576,272)	(192,773)	(1,553,619)	(448,913)
Transfers out of Level 3		116,237	657,059	396,665
Balance, end of period	(2,993,341)	(2,155,561)	(2,993,341)	(2,155,561)
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	(33,245)	166,532	(148,573)	63,605
Investment by class [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	63,770	183,433	97,522	199,172
Included in earnings	(22)		17
Included in other comprehensive income	471	(47)	6,697	(3,419)
Purchases		(8,451)		(541)
Issuances
Settlements	(3,497)		(96,118)	(16,600)
Transfers in Level 3		(2,099)	58,905	(5,776)
Transfers out of Level 3			(6,301)
Deconsolidation of VIEs		(75,483)		(75,483)
Balance, end of period	60,722	97,353	60,722	97,353
Investment by class [Member] | Other Asset Backed Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	50,746	159,768	75,886	159,473
Included in other comprehensive income	122		6,498
Purchases		(8,719)		(6,931)
Issuances
Settlements	(573)		(85,157)
Transfers in Level 3			53,068	(1,493)
Transfers out of Level 3		(75,483)
Deconsolidation of VIEs				(75,483)
Balance, end of period	50,295	75,566	50,295	75,566
Investment by class [Member] | U.S. Agency Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period		984	1,224	1,197
Included in earnings			(2)
Included in other comprehensive income		(10)	(9)	(3)
Purchases				(7)
Issuances
Settlements			(749)
Transfers in Level 3				(213)
Transfers out of Level 3			(464)
Balance, end of period		974		974
Derivatives by class [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	(507,604)	(262,287)	(486,775)	(195,934)
Included in earnings	26,285	(297,927)	67,322	(328,205)
Issuances
Settlements	7,278	70,241	(54,588)	34,166
Balance, end of period	(474,041)	(489,973)	(474,041)	(489,973)
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	22,792	(275,099)	(51,611)	(323,400)
Collateralized debt obligations [Member] | Investment by class [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	9,558	14,713	12,482	30,433
Included in earnings	(2)		(5)
Included in other comprehensive income	200	(2)	492	(3,284)
Purchases		52		6,185
Issuances
Settlements	(2,924)		(6,137)	(16,600)
Transfers in Level 3		(2,099)		(4,070)
Balance, end of period	6,832	12,664	6,832	12,664
Corporate Obligations [Member] | Investment by class [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	3,466	7,968	7,930	8,069
Included in earnings	(20)		24
Included in other comprehensive income	149	(45)	(284)	(132)
Purchases		226		212
Issuances
Settlements			(4,075)
Transfers in Level 3			5,837
Transfers out of Level 3			(5,837)
Balance, end of period	3,595	8,149	3,595	8,149
Interest Rate Swaps [Member] | Derivatives by class [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	(295,987)	(67,210)	(302,177)	25,750
Included in earnings	(1,156)	(295,523)	(46,191)	(361,955)
Issuances
Settlements	10,223	74,070	61,448	47,542
Balance, end of period	(286,920)	(288,663)	(286,920)	(288,663)
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	(1,156)	(257,764)	(47,419)	(327,371)
Credit Derivative [Member] | Derivatives by class [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	(211,617)	(215,847)	(190,653)	(221,684)
Included in earnings	27,441	4,506	12,803	19,890
Issuances
Settlements	(2,945)	(3,829)	(9,271)	(13,376)
Balance, end of period	(187,121)	(215,170)	(187,121)	(215,170)
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	23,948	(10,425)	(4,192)	(9,889)
Call Option On Long Term Debt [Member] | Derivatives by class [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period		20,770	6,055
Included in earnings		(6,910)	100,710	13,860
Issuances
Settlements			(106,765)
Balance, end of period		13,860		13,860
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date		(6,910)		13,860
Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	63,770	183,433	97,522	199,172
Included in earnings	(22)	(47)	17	(3,419)
Included in other comprehensive income	471	(8,451)	6,697	(541)
Issuances
Sales				(16,600)
Settlements	(3,497)	(2,099)	(96,118)	(5,776)
Transfers in Level 3			58,905
Transfers out of Level 3		(75,483)	(6,301)	(75,483)
Balance, end of period	60,722	97,353	60,722	97,353
Other Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	15,792	18,451	16,779	17,909
Included in earnings	(771)	(1,119)	(1,758)	(577)
Issuances
Balance, end of period	15,021	17,332	15,021	17,332
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	(771)	(1,119)	(1,758)	(577)
Derivatives Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Balance, beginning of period	(507,604)	(262,287)	(486,775)	(195,934)
Included in earnings	26,285	(297,927)	67,322	(328,205)
Issuances
Settlements	7,278	(70,241)	(54,588)	34,166
Balance, end of period	(474,041)	(489,973)	(474,041)	(489,973)
The amount of total gains/(losses) included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the reporting date	$ 22,792	$ (275,099)	$ (51,611)	$ (323,400)