Segment Reporting (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Summarized financial information concerning our reportable segments
Gross Revenue	$ 2,492.3	$ 2,480.9	$ 4,819.5	$ 4,810.7
Intercompany Revenue	(405.7)	(414.5)	(768.0)	(786.6)
Net Revenue	2,086.6	2,066.4	4,051.5	4,024.1
Depreciation, amortization and depletion	208.6	213.8	414.4	416.8
Operating income	401.2	400.8	777.4	782.1
Capital Expenditures	184.5	177.0	481.7	385.4
Total Assets	19,682.0	19,571.4	19,682.0	19,571.4
Reportable Segments [Member]
Summarized financial information concerning our reportable segments
Depreciation, amortization and depletion	228.1	234.0	453.6	457.2
Eastern [Member]
Summarized financial information concerning our reportable segments
Gross Revenue	633.4	626.6	1,217.3	1,211.9
Intercompany Revenue	(96.3)	(94.4)	(178.9)	(177.6)
Net Revenue	537.1	532.2	1,038.4	1,034.3
Depreciation, amortization and depletion	47.6	52.9	99.0	104.5
Operating income	136.7	122.6	254.4	250.8
Capital Expenditures	54.4	43.9	114.3	85.0
Total Assets	4,450.7	4,481.6	4,450.7	4,481.6
Midwestern [Member]
Summarized financial information concerning our reportable segments
Gross Revenue	571.3	567.5	1,076.6	1,070.8
Intercompany Revenue	(104.5)	(109.8)	(190.9)	(198.2)
Net Revenue	466.8	457.7	885.7	872.6
Depreciation, amortization and depletion	54.8	54.7	106.4	106.6
Operating income	96.4	100.7	176.8	189.5
Capital Expenditures	60.0	60.1	115.2	121.4
Total Assets	3,798.9	3,665.3	3,798.9	3,665.3
Southern [Member]
Summarized financial information concerning our reportable segments
Gross Revenue	594.6	584.7	1,165.4	1,150.3
Intercompany Revenue	(80.4)	(81.6)	(156.6)	(157.6)
Net Revenue	514.2	503.1	1,008.8	992.7
Depreciation, amortization and depletion	57.2	57.4	112.0	115.0
Operating income	110.3	119.7	229.9	240.3
Capital Expenditures	45.2	46.3	105.6	84.8
Total Assets	4,876.7	4,845.5	4,876.7	4,845.5
Western [Member]
Summarized financial information concerning our reportable segments
Gross Revenue	664.1	671.1	1,306.1	1,315.7
Intercompany Revenue	(120.2)	(124.8)	(233.4)	(243.6)
Net Revenue	543.9	546.3	1,072.7	1,072.1
Depreciation, amortization and depletion	55.7	56.2	111.0	105.6
Operating income	117.9	131.3	240.9	261.9
Capital Expenditures	56.6	57.2	123.9	93.2
Total Assets	5,498.4	5,479.9	5,498.4	5,479.9
Corporate entities [Member]
Summarized financial information concerning our reportable segments
Gross Revenue	28.9	31.0	54.1	62.0
Intercompany Revenue	(4.3)	(3.9)	(8.2)	(9.6)
Net Revenue	24.6	27.1	45.9	52.4
Depreciation, amortization and depletion	12.8	12.8	25.2	25.5
Operating income	(60.1)	(73.5)	(124.6)	(160.4)
Capital Expenditures	(31.7)	(30.5)	22.7	1.0
Total Assets	$ 1,057.3	$ 1,099.1	$ 1,057.3	$ 1,099.1