Contractual Commitments Contractual Commitments (Details) - USD ($) $ in Millions	3 Months Ended	72 Months Ended
	Sep. 30, 2017	Sep. 01, 2023	Dec. 31, 2016
Other Commitments [Line Items]
Self-Insurance Reserve	$ 193		$ 179
Deferred compensation liability	39		40
Trust for Benefit of Employees [Member]
Other Commitments [Line Items]
Assets Held-in-trust	67		$ 62
NV Energy Exit
Other Commitments [Line Items]
Business Exit Costs	48
Other Accrued Liabilities, Current	38
NV Energy Exit | Subsidiary of Common Parent [Member]
Other Commitments [Line Items]
Business Exit Costs	33
Other Accrued Liabilities, Current	26
NV Energy Exit | Limited Liability Company [Member]
Other Commitments [Line Items]
Business Exit Costs	$ 15
Scenario, Forecast [Member] | NV Energy Exit | Subsidiary of Common Parent [Member]
Other Commitments [Line Items]
Business Exit Costs		$ 24
Business Exit Costs Fair Value		19
Scenario, Forecast [Member] | NV Energy Exit | Limited Liability Company [Member]
Other Commitments [Line Items]
Business Exit Costs		32
Business Exit Costs Fair Value		$ 26