Revenues Performance Obligations (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Revenue, Performance Obligation Satisfied over Time [Abstract]
Fixed Fee Revenues Recognized	$ 868.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	3 months
Estimated revenues from contracts with customers from unsatisfied performance obligations as of September 30, 2019 (1)	$ 1,130.5	[1]
Operating revenues which are fixed and determinable (operating leases) (1)	20.0	[1]
Total projected operating revenues under committed firm agreements as of September 30, 2019 (1)	$ 1,150.5	[1]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Estimated revenues from contracts with customers from unsatisfied performance obligations as of September 30, 2019 (1)	$ 1,009.0	[1]
Operating revenues which are fixed and determinable (operating leases) (1)	20.5	[1]
Total projected operating revenues under committed firm agreements as of September 30, 2019 (1)	$ 1,029.5	[1]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	22 years
Estimated revenues from contracts with customers from unsatisfied performance obligations as of September 30, 2019 (1)	$ 7,964.0	[1]
Operating revenues which are fixed and determinable (operating leases) (1)	188.5	[1]
Total projected operating revenues under committed firm agreements as of September 30, 2019 (1)	8,152.5	[1]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated revenues from contracts with customers from unsatisfied performance obligations as of September 30, 2019 (1)	10,103.5	[1]
Operating revenues which are fixed and determinable (operating leases) (1)	229.0	[1]
Total projected operating revenues under committed firm agreements as of September 30, 2019 (1)	$ 10,332.5	[1]

[1] For the 2019 period, $868.3 million represents actual fixed fee revenues recognized for the fulfillment of performance obligations during the nine months ended September 30, 2019.