Short-term Borrowings and Long-term Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]
Short-term Debt	$ 38	[1]	$ 62	[1]
Long-term Debt	0		0
Long-term Debt, Excluding Current Maturities	2,276		2,919
Long-term Debt, Current Maturities	365	[1]	0	[1]
Short Term Borrowings And Current Portion Long Term Debt	403	[1]	62	[1]
Long-term Debt, Maturities in 2013	365
Long-term Debt, Maturities in 2014	160
Long-term Debt, Maturities in 2015	0
Long-term Debt, Maturities in 2016	325
Long-term Debt, Maturities in 2017	250
Inventory financing [Member]
Debt Instrument [Line Items]
Short-term Debt	38	[1]	62	[1]
Long-term Debt	0		0
Line of Credit [Member] | CERC Corp [Member]
Debt Instrument [Line Items]
Size of Facility	950		950
Loans	0		0
Letters of Credit	0		0
Commercial Paper	0		285
Line of Credit Facility, Interest Rate Description	London Interbank Offered Rate plus 150 basis points
Percentage on limitation of debt to total capitalization under covenant (in hundredths)	65.00%
Senior notes 2013 to 2041 [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	2,328		2,693
Long-term Debt, Current Maturities	365	[1]	0	[1]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	4.50%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	7.875%
Commercial Paper [Member]
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	0	[2]	285	[2]
Long-term Debt, Current Maturities	0	[1],[2]	0	[1],[2]
Unamortized Discount Premium Member
Debt Instrument [Line Items]
Long-term Debt, Excluding Current Maturities	(52)		(59)
Long-term Debt, Current Maturities	$ 0	[1]	$ 0	[1]

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

[2] 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.