Summary of Accounting Policies - Redeemable Non Controlling Interest (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Redeemable Noncontrolling Interest [Roll Forward]
Balance at beginning of period	$ 138	$ 42
Net income (loss) attributable to redeemable noncontrolling interests	19	22
Other comprehensive income (loss)	(10)	(3)
Acquisition and other	17	0
Purchase accounting measurement period adjustment	(8)	0
Dividends declared	(17)	(33)
Balance at end of period	$ 139	$ 28