Selected Quarterly Financial Data (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]
Total revenues	$ 8,397	$ 8,275	$ 7,401	$ 7,908	$ 8,063	$ 8,013	$ 7,834	$ 7,671	$ 31,981	$ 31,581	$ 30,282
Total expenses	6,781	7,289	7,486	7,188	6,989	7,581	7,169	6,704	28,744	28,443	27,321
Income before income taxes	1,616	986	(85)	720	1,074	432	665	967	3,237	3,138	2,961
Income tax expense (benefit)	306	159	(45)	120	201	36	108	171	540	516	438
Net income	$ 1,310	$ 827	$ (40)	$ 600	$ 873	$ 396	$ 557	$ 796	$ 2,697	$ 2,622	$ 2,523
Net income per common share, basic (in dollars per share)	$ 5.13	$ 3.24	$ (0.16)	$ 2.34	$ 3.37	$ 1.52	$ 2.11	$ 3.01	$ 10.56	$ 10.01	$ 9.37
Net income per common share, diluted (in dollars per share)	$ 5.10	$ 3.23	$ (0.16)	$ 2.33	$ 3.35	$ 1.50	$ 2.10	$ 2.99	$ 10.52	$ 9.92	$ 9.28