Debt (Debt Maturities) (Details) $ in Millions	Dec. 31, 2018 USD ($)	[1]
Debt [Abstract]
Long-term debt, due 2019	$ 4
Long-term debt, due 2020	305
Long-term debt, due 2021	68
Long-term debt, due 2022	381
Long-term debt, due 2023	420
Long-term debt, due Thereafter	$ 4,856

[1] Excludes interest rate swap gains and bond discounts.