Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information [Abstract]
Total revenues	$ 11,878	$ 11,061	$ 10,979	$ 11,080	$ 11,445	$ 10,839	$ 10,571	$ 10,455	$ 44,998	$ 43,310	$ 40,604
Operating income	1,234	1,471	1,541	1,476	1,137	1,440	1,450	1,282	5,722	5,309	4,888
Net income	751	870	939	908	640	795	782	671	3,468	2,888	4,536
Net income attributable to common stockholders	$ 751	$ 870	$ 939	$ 908	$ 640	$ 795	$ 782	$ 671	$ 3,468	$ 2,888	$ 4,481
Earnings per share - basic (in USD per share)	$ 0.88	$ 1.02	$ 1.10	$ 1.07	$ 0.75	$ 0.94	$ 0.92	$ 0.78	$ 4.06	$ 3.40	$ 5.39
Earnings per share - diluted (in USD per share)	$ 0.87	$ 1.01	$ 1.09	$ 1.06	$ 0.75	$ 0.93	$ 0.92	$ 0.78	$ 4.02	$ 3.36	$ 5.20
Weighted average shares outstanding - basic (in shares)	856,294,467	854,578,241	854,368,443	851,223,498	849,102,785	847,087,120	847,660,488	855,222,664	854,143,751	849,744,152	831,850,073
Weighted average shares outstanding - diluted (in shares)	864,158,739	862,690,751	860,135,593	858,643,481	856,344,347	853,852,764	852,040,670	862,244,084	863,433,511	858,290,174	871,787,450