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
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share:
Net income available to common shareholders	$ 674	$ 29
Less: Income allocated to participating securities	2	1
Net income allocated to common shareholders	$ 672	$ 28
Average shares	714,432,813	713,555,693
Earnings per share (in dollars per share)	$ 0.94	$ 0.04
Earnings Per Diluted Share:
Net income available to common shareholders	$ 674	$ 29
Stock-based awards	0	0
Less: Income allocated to participating securities	2	1
Net income allocated to common shareholders	$ 672	$ 28
Average shares, stock based awards	9,000,000	6,000,000
Average shares	723,425,111	720,362,697
Earnings per diluted share (in dollars per share)	$ 0.93	$ 0.04