Income Taxes - Components of income tax expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of income tax expense (benefit)
Current	$ 1,499	$ 991	$ 704
Deferred	(116)	251	(236)
Total income tax expense	$ 1,383	$ 1,242	$ 468