Short-term Borrowings and Long-term Debt (Details) - USD ($) $ in Millions			12 Months Ended
		May 01, 2016	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Short-term Debt	[1]		$ 35	$ 40
Unamortized issuance costs, net			(10)	(12)
Unamortized discount (premium), net			(27)	(34)	[2]
Long-term Debt, Excluding Current Maturities			2,125	2,016	[2]
Long-term Debt, Current Maturities	[1]		250	325
Debt, Current	[1]		285	365
Size of Facility			600	600
Long-term Debt, Maturities in 2017			250
Long-term Debt, Maturities in 2018			300
Long-term Debt, Maturities in 2019			0
Long-term Debt, Maturities in 2020			0
Long-term Debt, Maturities in 2021			1,162
Inventory financing [Member]
Debt Instrument [Line Items]
Short-term Debt	[1],[3]		35	40
Senior Notes [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount		$ 325
Debt Instrument, Interest Rate, Stated Percentage Rate Range		6.15%
Senior Notes 4.50% to 6.625% due 2016 to 2041
Debt Instrument [Line Items]
Long-term Debt, Gross, Noncurrent			1,593	1,843	[2]
Long-term Debt, Gross, Current	[1]		250	325
Commercial Paper [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross, Noncurrent	[4]		569	219	[2]
Long-term Debt, Gross, Current	[1],[4]		$ 0	0
Line of Credit [Member]
Debt Instrument [Line Items]
Percentage on limitation of debt to total capitalization under covenant (in hundredths)			65.00%
Ratio of Indebtedness to Net Capital			0.358
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Loans			$ 0	0
Letter of Credit [Member]
Debt Instrument [Line Items]
Loans			4	2
Commercial Paper [Member]
Debt Instrument [Line Items]
Loans	[5]		$ 569	$ 219
Debt, Weighted Average Interest Rate			1.03%	0.81%
London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate Description	[6]		1.25%
Minimum [Member] | Senior Notes 4.50% to 6.625% due 2016 to 2041
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range			4.50%
Maximum [Member] | Senior Notes 4.50% to 6.625% due 2016 to 2041
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range			6.625%

[1] Includes amounts due or exchangeable within one year of the date noted.

[2] Includes $12 million of unamortized debt issuance costs to reflect adoption of ASU 2015-03.

[3] NGD currently has AMAs associated with its utility distribution service in Arkansas, north Louisiana and Oklahoma that extend through 2020. Pursuant to the provisions of the agreements, NGD sells natural gas and agrees to repurchase an equivalent amount of natural gas during the winter heating seasons at the same cost, plus a financing charge. These transactions are accounted for as an inventory financing.

[4] Classified as long-term debt because the termination date of the facility that backstops the commercial paper is more than one year from the date noted.

[5] Weighted average interest rate was approximately 1.03% and 0.81% as of December 31, 2016 and 2015, respectively.

[6] Based on current credit ratings.