Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Total revenues	$ 23,373	$ 23,251	$ 22,944	$ 22,537	$ 22,682	$ 22,426	$ 22,407	$ 22,525	$ 92,105	$ 90,040	$ 84,863
Income before income taxes	542	1,242	1,504	1,780	126	1,119	1,205	1,514	5,068	3,964	4,555
Net income	$ 424	$ 960	$ 1,054	$ 1,312	$ 1,232	$ 747	$ 855	$ 1,009	$ 3,750	$ 3,843	$ 2,470
Basic net income per share	$ 1.64	$ 3.70	$ 4.07	$ 5.13	$ 4.80	$ 2.87	$ 3.23	$ 3.82	$ 14.53	$ 14.70	$ 9.39
Diluted net income per share	$ 1.61	$ 3.62	$ 3.98	$ 4.99	$ 4.67	$ 2.80	$ 3.16	$ 3.73	$ 14.19	$ 14.35	$ 9.21