Commitments and Contingencies - Investments in Affiliates and Other Entities (Details) $ in Millions	51 Months Ended
Dec. 31, 2018 USD ($)	Dec. 31, 2014 kV substation km
EPC Electric Transmission Project
Other Commitments [Line Items]
Outstanding capital commitment expected to be paid in 2019	$ 8.6
Length of electrical transmission line to be constructed under contract \| km		500
Number of substations \| substation		2
Voltage of substations \| kV		500
Aggregate contributions to this unconsolidated affiliate	76.2
Proceeds from return of capital	59.3
Capital for Infrastructure Projects
Other Commitments [Line Items]
Outstanding capital commitment	80.0
Other Commitments, Planned Oil and Gas Infrastructure Projects
Other Commitments [Line Items]
Outstanding capital commitment	14.8
Outstanding capital commitment expected to be paid in 2019	14.1
Outstanding capital commitment anticipated to be paid between years two through four	0.7
Infrastructure Investors Partnership \| Capital for Infrastructure Projects
Other Commitments [Line Items]
Outstanding capital commitment	$ 1,000.0

Length of transmission line.

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- Definition

Number of Substations

+ References

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- Definition

Other Commitment, Due Years Two Through Four

+ References

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Voltage Of Substations

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- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

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Minimum amount of other commitment maturing in the next fiscal year following the latest fiscal year for commitments not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in this taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

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Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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