Commitments and Contingencies Purchase Commitments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Long-term Purchase Commitment [Line Items]
Current Fiscal Year End Date	--12-31
Long-term Purchase Commitment, Amount	$ 205
Long-term Purchase Commitment, Description	November 2019
Maximum [Member]
Long-term Purchase Commitment [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Minimum [Member]
Long-term Purchase Commitment [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	0.00%