Fair Value Measurements (Fair Value And Maximum Future Funding Commitments Related To Investments) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	225	205
Real estate	292	270
Distressed	192	182
Mezzanine	284	195
Traditional	711	565
Vintage	14	18
Investment funds	395	378
Total of alternative investments	2,113	1,813
Maximum Future Funding Commitments
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	111	141
Real estate	62	96
Distressed	152	57
Mezzanine	279	282
Traditional	587	200
Vintage		1
Investment funds
Total of alternative investments	1,191	777
Expected Liquidation Period Lower Range
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Liquidation period for financial alternative investments	5 years	5 years
Liquidation period for real estate alternative investments	3 years	3 years
Liquidation period for distressed alternative investments	6 years	6 years
Liquidation period for mezzanine alternative investments	6 years	6 years
Liquidation period for traditional alternative investments	3 years	3 years
Liquidation period for vintage alternative investments	1 year	1 year
Expected Liquidation Period Upper Range
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Liquidation period for financial alternative investments	9 years	9 years
Liquidation period for real estate alternative investments	9 years	9 years
Liquidation period for distressed alternative investments	9 years	9 years
Liquidation period for mezzanine alternative investments	9 years	9 years
Liquidation period for traditional alternative investments	8 years	8 years
Liquidation period for vintage alternative investments	3 years	3 years