Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Cash distributions			$ 2,275	$ 1,425
Related Party Transaction Revenue with Affiliates	$ 33	$ 31	67	68
Related Party Transaction Expenditures from Transactions with Related Party	$ 97	$ 82	$ 186	161
Equity Method Investments and Joint Ventures [Abstract]
Ownership Percentage in TTX Company	17.30%		17.30%
Investments related to TTX	$ 585		$ 585		$ 554
Parent Company
Related Party Transaction [Line Items]
Cash distributions			2,300	1,400
Tax Refund From Parent			217	0
Tax payments to parent company			347	$ 91
Receivable from parent company	31		31		235
Payable to parent company	53		53		$ 19
Earliest Tax Year [Member] | Parent Company
Related Party Transaction [Line Items]
Tax payable to parent related to prior year tax audits	$ 32		$ 32