Income Taxes - Reconciliation of unrecognized tax benefits (UTB) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Federal, State and Foreign Tax
Gross UTB Balance at January 1	$ 1,167	$ 647	$ 530
Additions based on tax positions related to the current year	74	76	129
Additions for tax positions of prior years	106	132	146
Additions related to recent acquisitions		396
Reductions for tax positions of prior years	(173)	(56)	(123)
Settlements	(8)	(4)	(17)
Reductions due to lapse of applicable statute of limitations	(53)	(24)	(18)
Gross UTB Balance at December 31	1,113	1,167	647
Net UTB that would impact the effective tax rate at December 31	$ 1,145	$ 1,178	$ 655