Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating Leases, Rent Expense			$ 73
Operating Lease, Cost	$ 37	$ 40
Variable Lease, Cost	19	27
Sublease Income	(1)	(2)
Lease, Cost	55	65
Operating Lease, Payments	30	39
Operating Lease, Right-of-Use Asset	$ 182	$ 207
Operating Lease, Weighted Average Remaining Lease Term	13 years	13 years
Operating Lease, Weighted Average Discount Rate, Percent	4.60%	4.61%
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 34
Lessee, Operating Lease, Liability, Payments, Due Year Two	28
Lessee, Operating Lease, Liability, Payments, Due Year Three	23
Lessee, Operating Lease, Liability, Payments, Due Year Four	19
Lessee, Operating Lease, Liability, Payments, Due Year Five	17
Lessee, Operating Lease, Liability, Payments, Due after Year Five	140
Lessee, Operating Lease, Liability, Payments, Due	261
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	72
Accounts Payable and Accrued Liabilities
Lessee, Lease, Description [Line Items]
Operating Lease, Liability, Current	28	$ 21
Regulatory liabilities, deferred income, and other [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Liability, Noncurrent	161	$ 188
Other Liabilities
Lessee, Lease, Description [Line Items]
Operating Lease, Liability	$ 189