Summary of Significant Accounting Policies - Redeemable Non Controlling Interest (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Redeemable Noncontrolling Interest [Roll Forward]
Balance at beginning of period	$ 196	$ 138
Net income (loss) attributable to redeemable noncontrolling interests	12	19
Other comprehensive income (loss)	(2)	(10)
Acquisition and other	0	17
Noncontrolling interest tender offer redemption	46	0
Redemption value measurement adjustment	10	0
Noncontrolling Interest, Period Increase (Decrease)	0	(8)
Reclassification of noncontrolling interest to permanent equity	(82)	0
Dividends declared	(25)	(17)
Balance at end of period	$ 63	$ 139