Fair Value Measurements (Fair Value And Maximum Future Funding Commitments Related To Investments) (Detail) (USD $) In Millions, unless otherwise specified					9 Months Ended
	Sep. 30, 2012 Fair Value [Member]	Dec. 31, 2011 Fair Value [Member]	Sep. 30, 2012 Maximum Future Funding Commitments [Member]	Dec. 31, 2011 Maximum Future Funding Commitments [Member]	Sep. 30, 2012 Expected Liquidation Period Lower Range [Member]	Sep. 30, 2011 Expected Liquidation Period Lower Range [Member]	Sep. 30, 2012 Expected Liquidation Period Upper Range [Member]	Sep. 30, 2011 Expected Liquidation Period Upper Range [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	$ 210	$ 205	$ 124	$ 141
Real estate	323	270	66	96
Distressed	189	182	142	57
Mezzanine	269	195	294	282
Traditional	647	565	541	200
Vintage	16	18	1	1
Investment funds	389	378
Total of alternative investments	$ 2,043	$ 1,813	$ 1,168	$ 777
Liquidation period for financial alternative investments (in years)					5 years	5 years	9 years	9 years
Liquidation period for real estate alternative investments (in years)					3 years	3 years	9 years	9 years
Liquidation period for distressed alternative investments (in years)					6 years	6 years	9 years	9 years
Liquidation period for mezzanine alternative investments (in years)					6 years	6 years	9 years	9 years
Liquidation period for traditional alternative investments (in years)					3 years	3 years	8 years	8 years
Liquidation period for vintage alternative investments (in years)					1 year	1 year	3 years	3 years