Variable Interest Entities - Investments by Ownership Percentage with Fair Value Election (Details) - Investment funds - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Fair value option investment funds	$ 716	$ 661
Greater than 3% – 49%
Variable Interest Entity [Line Items]
Fair value option investment funds	562	562
3% or less
Variable Interest Entity [Line Items]
Fair value option investment funds	$ 154	$ 99