Exit Costs - Transportation Commitments - Income Statement Disclosures (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Long-term Purchase Commitment [Line Items]
Revenue from Sales	$ 1,093	$ 1,230	$ 2,145	$ 2,516
Corporate
Long-term Purchase Commitment [Line Items]
Revenue from Sales	23	24	50	55
Purchased Gas
Long-term Purchase Commitment [Line Items]
Revenue from Sales	103	66	177	119
Cost of Purchased Oil and Gas	113	71	200	128
Purchased Gas | Corporate
Long-term Purchase Commitment [Line Items]
Revenue from Sales	23	24	50	55
Cost of Purchased Oil and Gas	37	31	49	53
Cost of Purchased of Gas
Long-term Purchase Commitment [Line Items]
Cost of Purchased Oil and Gas			200	128
Cost of Purchased of Gas | Corporate
Long-term Purchase Commitment [Line Items]
Cost of Purchased Oil and Gas	22	23	79	67
Utilized Firm Transportation Expense | Corporate
Long-term Purchase Commitment [Line Items]
Cost of Purchased Oil and Gas	15	6	30	11
Unutilized Firm Transportation Expense | Corporate
Long-term Purchase Commitment [Line Items]
Cost of Purchased Oil and Gas	$ 0	$ 2	$ 0	$ 3