Leases (Lease Costs) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Amortization of right-of-use assets	$ 20
Interest on lease liabilities	6
Total finance lease cost	26
Operating lease cost	531
Short-term lease cost	118
Variable lease cost	12
Sublease income	(16)
Total net lease cost	$ 671