Leases Lease-Related Assets and Liabilities (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Finance Lease, Right of Use Asset, Accumulated Depreciation	$ 372,000,000
Operating lease right-of-use assets	1,508,000,000	$ 0
Finance lease right-of-use asset	890,000,000
Less allowance for depreciation and amortization	9,875,000,000	9,731,000,000
Total lease assets	2,398,000,000
Current operating lease liabilities	361,000,000	0
Finance lease, current maturities of long-term debt	85,000,000
Noncurrent operating lease liabilities	1,150,000,000	$ 0
Finance lease, long-term debt less current maturities	630,000,000
Total lease liabilities	2,226,000,000
Finance Lease
Finance lease, current maturities of long-term debt	85,000,000
Finance lease, long-term debt less current maturities	$ 630,000,000