Leases Components of lease expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Finance lease cost - Amortization of right-of-use assets	$ 19
Finance lease cost - Interest on lease liabilities	51
Operating lease cost	355
Short-term lease cost	110
Sublease income	(5)
Total lease cost	$ 530
Operating Leases, Rent Expense, Net		$ 680	$ 574