Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Current assets and current liabilities [Abstract]
Threshold for components of total current assets and liabilities to be presented as an individual caption on Consolidated Balance Sheet (in hundredths)	5.00%		5.00%
Deferred revenues [Abstract]
Deferred revenues	$ 122.7		$ 113.9
Environmental costs [Abstract]
Environmental reserves - current portion	4.5		3.7
Liquids exchange contracts [Abstract]
Liquids exchange balance, payables	301.7		144.1
Natural gas imbalance [Abstract]
Natural gas imbalance receivables	17.2	[1]	22.8	[1]
Natural gas imbalance payables	24.0	[2]	31.9	[2]
Restricted cash [Abstract]
Restricted cash	38.5		98.7
Fair Value [Member]
Financial Liabilities:
Fixed-rate debt (principal amount)	15,760		12,910
Carrying Value [Member]
Financial Liabilities:
Fixed-rate debt (principal amount)	14,330		12,030
Allowance for Doubtful Accounts, Current [Member]
Movement in valuation allowances and reserves [Roll Forward]
Balance at beginning of period	18.4		16.8		17.7
Charged to costs and expenses	0.8		2.6		0.1
Acquisition-related additions and other	0		1.1		0
Deductions	(5.8)	[3]	(2.1)	[3]	(1.0)	[3]
Balance at end of period	13.4		18.4		16.8
Reserve for Environmental Costs [Member]
Movement in valuation allowances and reserves [Roll Forward]
Balance at beginning of period	12.4		16.7		22.3
Charged to costs and expenses	9.3		2.8		1.9
Acquisition-related additions and other	1.0		0.9		0
Deductions	(10.4)		(8.0)		(7.5)
Balance at end of period	$ 12.3		$ 12.4		$ 16.7

[1] Reflected as a component of "Accounts receivable - trade" on our Consolidated Balance Sheets.

[2] Reflected as a component of "Accrued product payables" on our Consolidated Balance Sheets.

[3] The 2011 deduction amount is primarily due to our reassessment of the allowance for doubtful accounts as a result of improved credit ratings of a significant customer, which reduced our exposure to potential uncollectibility.