Income Taxes (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal and foreign									$ 686,000,000	$ 734,000,000	$ 738,000,000
State and local									115,000,000	114,000,000	129,000,000
Total current									801,000,000	848,000,000	867,000,000
Deferred:
Federal and foreign									(103,000,000)	(170,000,000)	(209,000,000)
State and local									(20,000,000)	(19,000,000)	(19,000,000)
Total deferred									(123,000,000)	(189,000,000)	(228,000,000)
Income tax expense	$ 152,000,000	$ 159,000,000	$ 179,000,000	$ 188,000,000	$ 169,000,000	$ 171,000,000	$ 152,000,000	$ 167,000,000	$ 678,000,000	$ 659,000,000	$ 639,000,000
Effective income tax rate:
Federal statutory income tax rate (as a percent)									35.00%	35.00%	35.00%
State income taxes-net of federal effect (as a percent)									3.50%	3.60%	4.00%
Other (as a percent)									0.00%	(0.60%)	0.70%
Effective income tax rate (as a percent)									38.50%	38.00%	39.70%
Deferred tax liabilities:
Property, plant and equipment	(1,384,000,000)				(1,431,000,000)				$ (1,384,000,000)	$ (1,431,000,000)
Intangibles assets	(1,088,000,000)				(1,153,000,000)				(1,088,000,000)	(1,153,000,000)
Receivable from an affiliate due to pension plan participation	(452,000,000)				(460,000,000)				(452,000,000)	(460,000,000)
Other	0				(59,000,000)				0	(59,000,000)
Total deferred tax liabilities	(2,924,000,000)				(3,103,000,000)				(2,924,000,000)	(3,103,000,000)
Deferred tax assets:
Payable to affiliate due to post-retirement plan participation	954,000,000				921,000,000				954,000,000	921,000,000
Debt premiums	0				21,000,000				0	21,000,000
Other	209,000,000				277,000,000				209,000,000	277,000,000
Total deferred tax assets	1,163,000,000				1,219,000,000				1,163,000,000	1,219,000,000
Valuation allowance on deferred tax assets	(12,000,000)				(12,000,000)				(12,000,000)	(12,000,000)
Net deferred tax assets	1,151,000,000				1,207,000,000				1,151,000,000	1,207,000,000
Net deferred tax liabilities	(1,773,000,000)				(1,896,000,000)				(1,773,000,000)	(1,896,000,000)
Change in valuation allowance of deferred tax assets									0
Domestic tax authority
Income Tax Contingency [Line Items]
Liabilities recorded for interest related to uncertain tax positions	0				0				0	0	$ 0
Liabilities recorded for penalties related to uncertain tax positions	$ 0				$ 0				$ 0	$ 0	$ 0