Income Taxes - Components of income tax expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of income tax expense (benefit)
Current	$ 991	$ 704	$ 1,018
Deferred	251	(236)	(23)
Total income tax expense	$ 1,242	$ 468	$ 995