Long-Term Debt - Key Financial Covenants (Details) $ in Billions	12 Months Ended
	Dec. 31, 2017 USD ($)
Pacific Facilities
Debt Instrument [Line Items]
Minimum fixed charge coverage ratio	1.20
Minimum unrestricted liquidity, unrestricted cash, permitted investments and undrawn revolving credit facilities	$ 2.0
Minimum collateral coverage ratio	1.60
2015 Credit Facilities
Debt Instrument [Line Items]
Minimum unrestricted liquidity, unrestricted cash, permitted investments and undrawn revolving credit facilities	$ 2.0
Minimum collateral coverage ratio	1.60