Leases (Lease Cost) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 328	[1]
Amortization of leased assets	72
Interest on lease liabilities	34
Net lease cost	434
Short-term operating lease cost	1
Variable operating lease cost	$ 8

[1] Includes short-term lease costs of $1 million and variable lease costs of $8 million.