Fair Value Measurements (Fair Value And Maximum Future Funding Commitments Related To Investments) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Fair Value [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	$ 246	$ 225
Real estate	347	292
Distressed	180	192
Mezzanine	261	284
Traditional	750	711
Vintage	12	14
Investment funds	414	395
Total of alternative investments	2,210	2,113
Maximum Future Funding Commitments [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	94	111
Real estate	67	62
Distressed	130	152
Mezzanine	285	279
Traditional	568	587
Vintage	0	0
Total of alternative investments	$ 1,144	$ 1,191
Expected Liquidation Period Lower Range [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Liquidation period for financial alternative investments (in years)	5 years	5 years
Liquidation period for real estate alternative investments (in years)	3 years	3 years
Liquidation period for distressed alternative investments (in years)	6 years	6 years
Liquidation period for mezzanine alternative investments (in years)	6 years	6 years
Liquidation period for traditional alternative investments (in years)	3 years	3 years
Liquidation period for vintage alternative investments (in years)	1 year	1 year
Expected Liquidation Period Upper Range [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Liquidation period for financial alternative investments (in years)	9 years	9 years
Liquidation period for real estate alternative investments (in years)	9 years	9 years
Liquidation period for distressed alternative investments (in years)	9 years	9 years
Liquidation period for mezzanine alternative investments (in years)	9 years	9 years
Liquidation period for traditional alternative investments (in years)	8 years	8 years
Liquidation period for vintage alternative investments (in years)	3 years	3 years