Fair Value Disclosures (Narrative) (Detail) (USD $)	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	Dec. 31, 2011	Sep. 30, 2012 Collateralized Loan Obligations [Member]	Sep. 30, 2011 Collateralized Loan Obligations [Member]	Sep. 30, 2012 Assets Of Consolidated VIEs Bank Loans [Member]	Sep. 30, 2011 Assets Of Consolidated VIEs Bank Loans [Member]	Sep. 30, 2012 Assets Of Consolidated VIEs Bank Loans [Member]	Sep. 30, 2011 Assets Of Consolidated VIEs Bank Loans [Member]	Sep. 30, 2012 Total Level 3 assets [Member]	Sep. 30, 2012 Total Level 3 assets [Member]	Sep. 30, 2011 Total Level 3 assets [Member]	Sep. 30, 2012 Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2011 Significant Unobservable Inputs (Level 3) [Member]	Sep. 30, 2012 Separate Account Assets, Equity Securities [Member]	Sep. 30, 2011 Separate Account Assets, Equity Securities [Member]	Sep. 30, 2012 Separate Account Assets, Equity Securities [Member]	Sep. 30, 2011 Separate Account Assets, Equity Securities [Member]	Sep. 30, 2012 CLO Borrowings [Member]	Sep. 30, 2011 CLO Borrowings [Member]	Sep. 30, 2012 CLO Borrowings [Member]	Sep. 30, 2011 CLO Borrowings [Member]	Sep. 30, 2012 CLO Bank Loans [Member]	Sep. 30, 2011 CLO Bank Loans [Member]	Sep. 30, 2012 CLO Bank Loans [Member]	Sep. 30, 2011 CLO Bank Loans [Member]	Sep. 30, 2012 Private Equity Funds [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Total assets measured at fair value on a recurring basis	$ 152,600,000,000		$ 141,600,000,000
Investments	1,864,000,000		1,631,000,000										727,000,000	702,000,000
Private equity investments	90,000,000		106,000,000										90,000,000	85,000,000													60,000,000
Transfer into Level 3						36,000,000	23,000,000	89,000,000	46,000,000						34,000,000	9,000,000	9,000,000	9,000,000
Net transfers into Level 3 from Level 2 of debt securities held																		87,000,000
Transfer out of Level 3						24,000,000	11,000,000	86,000,000	27,000,000
Distributions of earnings from equity method investees	29,000,000	26,000,000								24,000,000	57,000,000	35,000,000
Other settlements				406,000,000	390,000,000
Gains (loss) on fair value assets																			$ 45,000,000	$ 36,000,000	$ 123,000,000	$ 2,000,000	$ 44,000,000	$ 24,000,000	$ 118,000,000	$ 33,000,000