Earnings Per Share - Reconciliation of Basic and Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Basic income per share:
Net income available to common shareholders	$ 121	$ 482
Weighted average number of common shares outstanding — basic (in shares)	248	278
Income/(loss) per weighted average common share — basic (in usd per share)	$ 0.49	$ 1.73
Diluted income per share:
Net income available to common shareholders	$ 121	$ 482
Weighted average number of common shares outstanding - diluted (in shares)	248	278
Incremental shares attributable to the issuance of equity compensation (treasury stock method) (in shares)	1	2
Weighted average number of common shares outstanding- dilutive (in shares)	249	280
Income/(loss) per weighted average common share — diluted (in usd per share)	$ 0.49	$ 1.72