Fair Value Measurements (Fair Value And Maximum Future Funding Commitments Related To Investments) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Fair Value [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	$ 249	$ 225
Real estate	342	292
Distressed	168	192
Mezzanine	243	284
Traditional	811	711
Vintage	12	14
Investment funds	415	395
Total of alternative investments	2,240	2,113
Maximum Future Funding Commitments [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	83	111
Real estate	78	62
Distressed	122	152
Mezzanine	285	279
Traditional	505	587
Vintage	0	0
Total of alternative investments	$ 1,073	$ 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