Quarterly Financial Data - Unaudited (Details) - USD ($) $ 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
Quaterly Financial Data Unaudited [Abstract]
Revenues	$ 5,839	$ 6,021	$ 5,893	$ 5,762	$ 6,206	$ 6,147	$ 5,878	$ 5,624	$ 23,515	$ 23,855	$ 21,387
Operating income	2,105	2,180	2,007	1,779	2,061	2,109	1,883	1,747	8,071	7,800	7,293
Net income	$ 1,424	$ 1,466	$ 1,338	$ 1,253	$ 1,372	$ 1,393	$ 1,309	$ 1,145	$ 5,481	$ 5,219	$ 11,300