Derivative Instruments, Hedging Activities and Fair Value Measurements, Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended												9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended								9 Months Ended				9 Months Ended				9 Months Ended				9 Months Ended				9 Months Ended
	Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Long-lived Assets Held and Used [Member]	Sep. 30, 2012 Long-lived Assets Held and Used [Member]	Mar. 31, 2012 Long-lived Assets Disposed of By Sale [Member]	Sep. 30, 2012 Long-lived Assets Disposed of By Sale [Member]	Sep. 30, 2012 Long-lived Assets Disposed of Other Than By Sale [Member]	Sep. 30, 2012 Long-lived Assets Disposed of Other Than By Sale [Member]	Sep. 30, 2012 Level 3 [Member]	Sep. 30, 2011 Level 3 [Member]	Sep. 30, 2012 Level 3 [Member]	Sep. 30, 2011 Level 3 [Member]	Sep. 30, 2012 Level 3 [Member] Liability commodity derivatives - Crude oil [Member]	Sep. 30, 2012 Level 3 [Member] Liability commodity derivatives - Normal butane [Member]	Sep. 30, 2012 Level 3 [Member] Liability commodity derivatives - Natural gasoline [Member]	Sep. 30, 2012 Level 3 [Member] Liability commodity derivatives - Natural gas [Member]	Sep. 30, 2012 Level 3 [Member] Liability commodity derivatives - Propane [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Propane [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Propane [Member] Liability commodity derivatives - Propane [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Propane [Member] Liability commodity derivatives - Propane [Member] Minimum [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Propane [Member] Liability commodity derivatives - Propane [Member] Maximum [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Normal butane [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Normal butane [Member] Liability commodity derivatives - Normal butane [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Normal butane [Member] Liability commodity derivatives - Normal butane [Member] Minimum [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Normal butane [Member] Liability commodity derivatives - Normal butane [Member] Maximum [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Crude oil [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Crude oil [Member] Liability commodity derivatives - Crude oil [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Crude oil [Member] Liability commodity derivatives - Crude oil [Member] Minimum [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Crude oil [Member] Liability commodity derivatives - Crude oil [Member] Maximum [Member]	Sep. 30, 2012 Level 3 [Member] Assets commodity derivatives - Natural gas [Member]	Sep. 30, 2012 Level 3 [Member] Assets commodity derivatives - Natural gas [Member] Liability commodity derivatives - Natural gas [Member]	Sep. 30, 2012 Level 3 [Member] Assets commodity derivatives - Natural gas [Member] Liability commodity derivatives - Natural gas [Member] Minimum [Member]	Sep. 30, 2012 Level 3 [Member] Assets commodity derivatives - Natural gas [Member] Liability commodity derivatives - Natural gas [Member] Maximum [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Natural gasoline [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Natural gasoline [Member] Liability commodity derivatives - Natural gasoline [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Natural gasoline [Member] Liability commodity derivatives - Natural gasoline [Member] Minimum [Member]	Sep. 30, 2012 Level 3 [Member] Asset commodity derivatives - Natural gasoline [Member] Liability commodity derivatives - Natural gasoline [Member] Maximum [Member]	Sep. 30, 2012 Fair Value [Member]	Dec. 31, 2011 Fair Value [Member]	Sep. 30, 2012 Carrying Value [Member]	Dec. 31, 2011 Carrying Value [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member] Level 1 [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member] Level 2 [Member]	Sep. 30, 2012 Fair Value, Measurements, Recurring [Member] Level 3 [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Long-lived Assets Held and Used [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Long-lived Assets Disposed of By Sale [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Long-lived Assets Disposed of Other Than By Sale [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 1 [Member] Long-lived Assets Held and Used [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 1 [Member] Long-lived Assets Disposed of By Sale [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 1 [Member] Long-lived Assets Disposed of Other Than By Sale [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 2 [Member] Long-lived Assets Held and Used [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 2 [Member] Long-lived Assets Disposed of By Sale [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 2 [Member] Long-lived Assets Disposed of Other Than By Sale [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 3 [Member] Long-lived Assets Held and Used [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 3 [Member] Long-lived Assets Disposed of By Sale [Member]	Sep. 30, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 3 [Member] Long-lived Assets Disposed of Other Than By Sale [Member]
Financial assets [Abstract]
Interest rate derivatives																																																						$ 45.1	$ 0	$ 45.1	$ 0
Commodity derivatives																					13.3		13.3							4.2				0.4				0.2				0.1				8.4								79.7	22.4	44.0	13.3
Long-lived fixed assets held for sale					0.5
Financial assets																																																						124.8	22.4	89.1	13.3	2.2	0	0	0	0	0	0	0	0	2.2	0	0
Non-cash asset impairment charges	43.1						5.2						57.6	5.2		2.6		0.3	40.5	54.7
Carrying value prior to impairment															4.8		0.8
Impairment of Long-Lived Assets to be Abandoned																			29.2	29.2
Financial liabilities [Abstract]
Interest rate derivatives																																																						200.0	0	200.0	0
Commodity derivatives																					4.1		4.1		0.9	0.7	1.5	0.3	0.7																									77.7	32.5	41.1	4.1
Financial liabilities																																																						277.7	32.5	241.1	4.1
Unrealized gain (loss) recognized as a component of net income related to level 3 financial assets and liabilities													15.9	6.8							0.8	0.7	(1.1)	2.5
Reconciliation of changes in the fair value of Level 3 financial assets and liabilities [Roll Forward]
Balance, beginning of period	4.9		0.9		0.4		2.1		0.4		(25.9)		0.4	(25.9)
Total gains (losses) included in:
Net income	(0.6)	[1]	(1.3)	[1]	0.5	[1]	0.8	[1]	1.9	[1]	(0.5)	[1]
Other comprehensive income (loss)	3.5		6.0		0.5		0		0		16.2
Settlements	1.4		(0.7)		(0.5)		(2.2)		(0.2)		0.8
Transfers out of Level 3					0						9.8	[2]
Balance, end of period	9.2		4.9		0.9		0.7		2.1		0.4		9.2	0.7
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Asset commodity derivatives																					13.3		13.3							4.2				0.4				0.2				0.1				8.4								79.7	22.4	44.0	13.3
Financial assets																																																						124.8	22.4	89.1	13.3	2.2	0	0	0	0	0	0	0	0	2.2	0	0
Liability commodity derivatives																					4.1		4.1		0.9	0.7	1.5	0.3	0.7																									77.7	32.5	41.1	4.1
Financial liabilities																																																						277.7	32.5	241.1	4.1
Fair Value Measurements, Valuation Techniques																															Discounted cash flow				Discounted cash flow				Discounted cash flow				Discounted cash flow				Discounted cash flow
Input description																															Forward prices in excess of 1 year				Forward prices in excess of 1 year				Pricing data relative to quality and location attributes of crude oil				Forward prices in excess of 3 years				Forward prices in excess of 1 year
Fair value inputs, forward commodity price (in dollars per unit)																																0.92	0.98			1.49	1.51			92.19	92.56			4.14	4.39			1.97	2.02
Financial Liabilities: [Abstract]
Fixed Rate Debt Principal Amount Fair Value Disclosure																																																		$ 18,000	$ 15,760	$ 15,830	$ 14,330

[1] There were $0.8 million of unrealized gains and $1.1 million of unrealized losses included in these amounts for the three and nine months ended September 30, 2012, respectively. There were $0.7 million and $2.5 million of unrealized gains included in these amounts for the three and nine months ended September 30, 2011, respectively.

[2] Transfers out of Level 3 into Level 2 during 2011 were primarily due to the change in observability of forward NGL prices.