Regulatory Matters - Regulatory Liabilities (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Federal statutory income tax rate		21.00%	21.00%	35.00%
Regulatory liabilities		$ 211	$ 160
Regulatory liabilities, noncurrent		7,100	7,346
Regulatory Liabilities		7,311	7,506
Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[1]	$ 3,611	3,923
Weighted average remaining life	[1]	Various
Cost of removal
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[2]	$ 2,370	2,426
Weighted average remaining life	[2]	26.8240506329114
Asset retirement obligations
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 241	163
Weighted average remaining life		33
Levelized depreciation [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 304	329
Weighted average remaining life		29
Impact fees
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 72	88
Weighted average remaining life		2
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities		$ 713	$ 577
Weighted average remaining life		Various
Tax Cuts and Jobs Act of 2017 [Member]
Regulatory Liabilities [Line Items]
Federal statutory income tax rate		21.00%	21.00%
Tax Cuts and Jobs Act of 2017 [Member] | Deferred Income Tax Charge [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities	[3]	$ 5,950

[1] (1)Amounts primarily represent income tax liabilities related to the federal tax rate change from 35% to 21% that are probable to be passed on to customers, offset by income tax benefits related to certain property-related basis differences and other various differences that were previously passed on to customers and will be included in regulated rates when the temporary differences reverse. See Note 12 for further discussion of 2017 Tax Reform impacts.

[2] Amounts represent estimated costs, as accrued through depreciation rates and exclusive of ARO liabilities, of removing regulated property, plant and equipment in accordance with accepted regulatory practices. Amounts are deducted from rate base or otherwise accrue a carrying cost.

[3] Amounts primarily represent income tax liabilities related to the federal tax rate change from 35% to 21% that are probable to be passed on to customers, offset by income tax benefits related to accelerated tax depreciation and certain property-related basis differences that were previously passed on to customers and will be included in regulated rates when the temporary differences reverse.