Selected Quarterly Financial Data (Unaudited) (details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Data (Unaudited) disclosure
Total revenues	$ 7,451	$ 7,325	$ 7,184	$ 6,942	$ 7,193	$ 6,961	$ 6,785	$ 6,686	$ 28,902	$ 27,625	$ 26,815
Total expenses	6,591	7,005	6,394	6,182	5,891	6,014	5,898	5,769	26,172	23,572	22,075
Income before income taxes	860	320	790	760	1,302	947	887	917	2,730	4,053	4,740
Income tax expense	309	27	195	143	359	231	223	226	674	1,039	1,301
Net income	$ 551	$ 293	$ 595	$ 617	$ 943	$ 716	$ 664	$ 691	$ 2,056	$ 3,014	$ 3,439
Net income per share, basic (in dollars per share)	$ 2.00	$ 1.06	$ 2.13	$ 2.19	$ 3.32	$ 2.48	$ 2.27	$ 2.33	$ 7.39	$ 10.39	$ 10.99
Net income per common share, diluted (in dollars per share)	$ 1.98	$ 1.05	$ 2.11	$ 2.17	$ 3.28	$ 2.45	$ 2.24	$ 2.30	$ 7.33	$ 10.28	$ 10.88
Net charge included in total income tax expense related to TCJA at the date of enactment	$ 129								$ 129