Quarterly Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 12,018	$ 11,500	$ 11,197	$ 10,076	$ 11,472	$ 11,069	$ 11,144	$ 10,990	$ 44,791	$ 44,675	$ 39,815
Net income (loss) applicable to common shareholders	$ 2,598	$ 1,126	$ 1,224	$ 513	$ 1,707	$ 889	$ 821	$ 1,261	$ 5,461	$ 4,678	$ 2,012
Earnings per common share - Basic (in dollars per share)	$ 8.54	$ 3.62	$ 3.90	$ 1.62	$ 5.32	$ 2.71	$ 2.47	$ 3.79	$ 17.53	$ 14.25	$ 5.78
Earnings per common share - Diluted (in dollars per share)	$ 8.45	$ 3.58	$ 3.86	$ 1.59	$ 5.23	$ 2.67	$ 2.44	$ 3.74	$ 17.31	$ 14.03	$ 5.70