Summary of Significant Accounting Policies - Redeemable Non Controlling Interest (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Redeemable Noncontrolling Interest [Roll Forward]
Balance at beginning of period	$ 196	$ 138
Net income (loss) attributable to redeemable noncontrolling interests	5	15
Other comprehensive income (loss)	(4)	1
Acquisition and other	0	16
Noncontrolling interest tender offer redemption	(46)	0
Noncontrolling interest tender offer redemption	10	0
Purchase accounting measurement period adjustment	0	(8)
Reclassification of noncontrolling interest to permanent equity	(82)	0
Dividends declared	0	(17)
Balance at end of period	$ 79	$ 145