Fair Value Disclosures - Investments in Certain Entities Calculate Net Asset Value per Share (Parenthetical) (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2017	Dec. 31, 2016
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total Unfunded Commitments	$ 287	$ 157
Hedge Funds/Funds of Hedge Funds [Member] \| Equity Method Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidation period, years	6 years	1 year
Total Unfunded Commitments	$ 11	$ 14
Private Equity Funds [Member] \| Equity Method Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidation period, years	5 years	5 years
Total Unfunded Commitments	$ 67	$ 62
Real Assets Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total Unfunded Commitments	167	56
Amount of unfunded commitments contractually obligated to fund	137	56
Real Assets Funds [Member] \| Consolidated Variable Interest Entities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total Unfunded Commitments	$ 54	$ 21
Real Assets Funds [Member] \| Equity Method Investments [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption period	8 years	6 years
Total Unfunded Commitments	$ 113	$ 35
Private Equity Funds Of Funds [Member] \| Consolidated Variable Interest Entities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Liquidation period, years	5 years	5 years
Total Unfunded Commitments	$ 20	$ 16
Amount of unfunded commitments contractually obligated to fund	$ 24	$ 24