Leases (Lease Cost) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 406
Finance lease cost:
Amortization of right-of-use assets	23
Interest expense on lease liabilities	3
Short-term lease cost	242
Variable lease cost	80
Sublease income	(31)
Total lease cost	$ 723