Leases (Maturity Analysis For Operating and Finance Lease Liabilities) (Details) $ in Millions	Dec. 31, 2019 USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Present value of lease liabilities	$ 211
Finance Lease, Liability, Payment, Due [Abstract]
Present value of lease liabilities	167
Northwest Operations [Member]
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Present value of lease liabilities	15
Finance Lease, Liability, Payment, Due [Abstract]
Present value of lease liabilities	28
Prior To Reclass To Assets Held-for-sale [Member]
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2020	50
2021	45
2022	42
2023	39
2024	34
Thereafter	88
Total lease payments	298
Less: imputed interest	(72)
Present value of lease liabilities	226
Finance Lease, Liability, Payment, Due [Abstract]
2020	44
2021	38
2022	33
2023	29
2024	21
Thereafter	102
Total lease payments	267
Less: imputed interest	(72)
Present value of lease liabilities	$ 195