Income Taxes - Reconciliation of unrecognized tax benefits (UTB) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Federal, State and Foreign Tax
Gross UTB Balance at January 1	$ 530	$ 319	$ 381
Additions based on tax positions related to the current year	129	119	67
Additions for tax positions of prior years	146	149	43
Reductions for tax positions of prior years	(123)	(38)	(66)
Settlements (UTB decreases)	(17)	(3)	(95)
Reductions due to lapse of applicable statute of limitations	(18)	(16)	(11)
Gross UTB Balance at December 31	$ 647	$ 530	$ 319