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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share:
Net income available to common shareholders	$ 674	$ 163	$ 1,348	$ 193
Less: Income allocated to participating securities	1	1	4	2
Net income allocated to common shareholders	$ 673	$ 162	$ 1,344	$ 191
Average shares	708,832,787	714,766,570	711,617,331	714,161,131
Earnings per share (in dollars per share)	$ 0.95	$ 0.23	$ 1.89	$ 0.27
Earnings Per Diluted Share:
Net income available to common shareholders	$ 674	$ 163	$ 1,348	$ 193
Stock-based awards	0	0	0	0
Less: Income allocated to participating securities	1	1	4	2
Net income allocated to common shareholders	$ 673	$ 162	$ 1,344	$ 191
Average shares, stock based awards	9,000,000	3,000,000	9,000,000	5,000,000
Average shares	718,084,745	717,571,890	720,740,176	718,967,293
Earnings per diluted share (in dollars per share)	$ 0.94	$ 0.23	$ 1.87	$ 0.27