Fair Value (Nonrecurring Unobservable Inputs) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Liabilities Value		$ (102)
Laurel Mountain [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring			$ 30
Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring			5
Fair Value | Level 3
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring		315
Long Lived Assets Held For Sale [Member] | Level 3 | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring		212
Long Lived Assets Held And Used [Member] | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring		103
Long Lived Assets Held And Used [Member] | Level 3 | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring		$ 103
Long Lived Assets Held And Used [Member] | Fair Value | Level 3 | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Assets Carrying Amount Disclosure Nonrecurring	[1]		$ 5
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		(11.00%)
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		(27.00%)
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		1.00%
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		41.00%
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		(6.00%)
Measurement Input, Long-term Revenue Growth Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		2.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		5.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		0.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		35.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		0.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		29.00%
Measurement Input, Operating Margin [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		0.00%
Measurement Input, Discount Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Minimum | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		5.00%
Measurement Input, Discount Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Maximum | Hawaii Subsidiary [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		15.00%
Measurement Input, Discount Rate [Member] | Valuation, Income Approach [Member] | Long Lived Assets Held And Used [Member] | Weighted Average | OPGC Affiliate [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Measurement Inputs, Nonrecurring		9.00%

[1] See Note 22—Asset Impairment Expense for further information.