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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share:
Net income available to common shareholders	$ 1,323	$ 2,419	$ 2,118
Less: Income allocated to participating securities	6	21	23
Net income allocated to common shareholders	$ 1,317	$ 2,398	$ 2,095
Average shares	714,729,585	710,433,611	673,346,168
Earnings per share (in dollars per share)	$ 1.84	$ 3.38	$ 3.11
Earnings Per Diluted Share:
Net income available to common shareholders	$ 1,323	$ 2,419	$ 2,118
Stock-based awards	0	0	0
Less: Income allocated to participating securities	6	21	23
Net income allocated to common shareholders	$ 1,317	$ 2,398	$ 2,095
Average shares, stock based awards	5,000,000	10,000,000	12,000,000
Average shares	719,735,415	720,065,498	685,488,498
Earnings per diluted share (in dollars per share)	$ 1.83	$ 3.33	$ 3.06