Leases - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) mi	Dec. 31, 2019 USD ($)		Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Right-of-use asset	$ 472	$ 532	[1]	$ 534
Right-of-use asset recognized as non-cash asset addition	11	51
Cash paid for amounts included in measurement of operating lease liabilities	$ 59	$ 60
State of Georgia
Lessee, Lease, Description [Line Items]
Term of lease agreement	50 years
Number of miles of right-of-way with integral equipment leased | mi	137
Percentage of annual increase in operating lease	2.50%
Maximum | Other parties
Lessee, Lease, Description [Line Items]
Term of lease agreement	50 years

[1] Certain prior year data has been reclassified to conform to the current presentation.