Earnings Per Share - Calculation of Earnings Per Share and the Reconciliation of Earnings Per Share to Earnings Per Diluted Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share:
Net income available to common shareholders	$ 163	$ 427	$ 193	$ 1,187
Less: Income allocated to participating securities	1	4	2	11
Net income allocated to common shareholders	$ 162	$ 423	$ 191	$ 1,176
Average shares	714,766,570	738,051,421	714,161,131	699,766,962
Earnings per share (in dollars per share)	$ 0.23	$ 0.57	$ 0.27	$ 1.68
Earnings Per Diluted Share:
Net income available to common shareholders	$ 163	$ 427	$ 193	$ 1,187
Stock-based awards	0	0	0	0
Less: Income allocated to participating securities	1	4	2	11
Net income allocated to common shareholders	$ 162	$ 423	$ 191	$ 1,176
Average shares, stock based awards	3,000,000	10,000,000	5,000,000	9,000,000
Average shares	717,571,890	747,749,591	718,967,293	709,430,194
Earnings per diluted share (in dollars per share)	$ 0.23	$ 0.57	$ 0.27	$ 1.66