Earnings Per Share Earnings Per Share - Schedule of Earnings per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income (loss) attributable to common shareholders	$ 152	$ 733	$ 539	$ 585	$ 1,880	$ 823	$ 95	$ 990	$ 2,010	$ 3,786	$ 1,121
Weighted average common shares outstanding — basic									967	947	924
Assumed exercise and/or distributions of stock-based awards									2	2	3
Weighted average common shares outstanding — diluted									969	949	927