Fair Value Measurements (Narrative) (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Fair Value Measurements Of Financial Instruments [Line Items]
Fair Value	$ 3,537	$ 2,477
Investment Funds Limited Partnerships Partially Owned Investment Companies Fair Value [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Fair Value	$ 3,537	2,477
Minimum [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Notice Period For Redemption For Alternative Investments Investment Funds	5 days
Maximum [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Notice Period For Redemption For Alternative Investments Investment Funds	120 days
Fair Value, Inputs, Level 2 [Member]
Fair Value Measurements Of Financial Instruments [Line Items]
Fair Value	$ 240	$ 230