Leases Components of lease expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Finance lease cost - Amortization of right-of-use assets	$ 19	$ 19
Finance lease cost - Interest on lease liabilities	32	51
Operating lease cost	296	355
Short-term lease cost	31	110
Sublease income	(4)	(5)
Total lease cost	$ 374	$ 530
Operating Leases, Rent Expense, Net			$ 680