Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Income Taxes.
Unrecognized tax benefits that would affect the effective tax rate	$ 1,090		$ 1,090		$ 1,145
Deferred tax assets valuation allowance	$ 150		$ 150		$ 135
Effective tax rate (as a percent)	21.50%	21.00%	18.90%	19.30%