Fair Value Measurements (Fair Value And Maximum Future Funding Commitments Related To Investments) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Minimum [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 assets alternative investments (in years)	3 years	3 years
Liquidation period for distressed alternative investments (in years)	5 years	5 years
Liquidation period for private credit alternative investments (in years)	3 years	3 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
Maximum [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 assets alternative investments (in years)	7 years	7 years
Liquidation period for distressed alternative investments (in years)	9 years	9 years
Liquidation period for private credit alternative investments (in years)	7 years	7 years
Liquidation period for traditional alternative investments (in years)	9 years	9 years
Liquidation period for vintage alternative investments (in years)	2 years	2 years
Fair Value [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	298	282
Real assets	478	464
Distressed	251	232
Private credit	303	299
Traditional	910	895
Vintage	9	11
Investment funds	383	378
Total of alternative investments	2,632	2,561
Maximum Future Funding Commitments [Member]
Fair Value And Maximum Future Funding Commitments Related To Investments [Line Items]
Financial	130	145
Real assets	193	214
Distressed	249	175
Private credit	181	190
Traditional	239	285
Vintage	0	1
Investment funds	0	0
Total of alternative investments	992	1,010