Fair Value Measurements (Fair Value And Maximum Future Funding Commitments Related To Investments) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 3,627	$ 2,477
Maximum future funding commitment	2,040	824
Financial
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	548	300
Maximum future funding commitment	$ 428	$ 105
Financial | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	5 years	5 years
Financial | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	9 years	9 years
Real Assets
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 536	$ 474
Maximum future funding commitment	$ 230	$ 140
Real Assets | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	3 years	3 years
Real Assets | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	7 years	7 years
Distressed
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 485	$ 261
Maximum future funding commitment	$ 179	$ 218
Distressed | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	5 years	5 years
Distressed | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	9 years	9 years
Private Credit
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 236	$ 265
Maximum future funding commitment	$ 259	$ 209
Private Credit | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	3 years	3 years
Private Credit | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	7 years	7 years
Traditional
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 1,550	$ 895
Maximum future funding commitment	$ 930	$ 152
Traditional | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	3 years	3 years
Traditional | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	9 years	9 years
Vintage
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 21	$ 13
Maximum future funding commitment	$ 14
Vintage | Minimum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	1 year	1 year
Vintage | Maximum
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Expected liquidation period	2 years	2 years
Investment Funds
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 251	$ 269