Discontinued Operations - Assets and Liabilities of Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents	$ 0	$ 11.9	$ 123.0	$ 0
Accounts receivable, net	599.4	316.3
Deferred income taxes - current	0	27.9
Prepaid expenses and other	50.8	45.4
Current assets of discontinued operations held for sale	138.3	122.0
Midstream field services	197.5	197.3
Material and supplies	55.3	54.3
Total Property, Plant and Equipment	13,191.5	12,573.6
Midstream field services	(34.3)	(28.1)
Other noncurrent assets	39.4	46.6
Noncurrent assets of discontinued operations held for sale	1,174.2	1,167.7
Production and property taxes	73.5	49.4
Interest payable	34.1	37.2
Current liabilities of discontinued operations held for sale	161.6	75.3
Long-term debt	3,115.5	2,997.5
Deferred income taxes	1,500.8	1,364.9
Asset retirement obligations	162.3	163.3
Other long-term liabilities	90.3	94.5
Noncurrent liabilities of discontinued operations held for sale	402.0	238.3
Midstream Business Held For Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and cash equivalents	27.1	18.1
Accounts receivable, net	71.8	53.9
Income taxes receivable	0	38.4
Deferred income taxes - current	7.0	2.7
Prepaid expenses and other	32.4	8.9
Current assets of discontinued operations held for sale	138.3	122.0
Midstream field services	1,550.5	1,500.8
Material and supplies	6.5	4.8
Total Property, Plant and Equipment	1,557.0	1,505.6
Midstream field services	(422.2)	(381.6)
Net Property, Plant and Equipment	1,134.8	1,124.0
Investment in unconsolidated affiliates	35.9	39.0
Other noncurrent assets	3.5	4.7
Noncurrent assets of discontinued operations held for sale	1,174.2	1,167.7
Accounts payable and accrued expenses	85.6	74.1
Accrued income taxes	70.2	0
Production and property taxes	5.4	1.2
Interest payable	0.4	0
Current liabilities of discontinued operations held for sale	161.6	75.3
Long-term debt	230.0	0
Deferred income taxes	126.5	195.7
Asset retirement obligations	29.9	28.5
Other long-term liabilities	15.6	14.1
Noncurrent liabilities of discontinued operations held for sale	$ 402.0	$ 238.3