Supplemental Guarantor/Non-Guarantor Financial Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Total revenues	$ 1,722.9	$ 1,797.6	$ 5,107.7	$ 5,270.9
Operating costs and expenses (exclusive of items shown separately below)	1,453.3	1,432.1	4,315.7	4,258.7
Depreciation, depletion and amortization	163.6	186.4	483.9	542.8
Asset retirement obligation expenses	15.0	13.4	46.5	50.7
Selling and administrative expenses	52.9	55.0	171.6	184.1
Other operating (income) loss:
Net gain on disposal or exchange of assets	(13.9)	(4.1)	(25.9)	(49.9)
Asset impairment	0	0	0	21.5
Loss (income) from equity affiliates and investment in subsidiaries	15.8	2.6	44.0	35.6
Interest expense	114.5	111.0	323.0	323.1
Interest income	(3.7)	(4.2)	(11.7)	(11.2)
Unrealized loss (gain) on derivatives		0		0
(Loss) income from continuing operations before income taxes	(74.6)	5.4	(239.4)	(84.5)
Income tax provision (benefit)	79.4	(18.6)	30.9	(199.6)
(Loss) income from continuing operations, net of income taxes	(154.0)	24.0	(270.3)	115.1
Income (loss) from discontinued operations, net of income taxes	5.0	(43.1)	6.0	(66.5)
Net (loss) income	(149.0)	(19.1)	(264.3)	48.6
Less: Net income attributable to noncontrolling interests	1.6	7.0	8.1	7.8
Net (loss) income attributable to common stockholders	(150.6)	(26.1)	(272.4)	40.8
Other comprehensive (loss) income, net of income taxes	(207.6)	14.1	(7.2)	(416.9)
Comprehensive (loss) income	(356.6)	(5.0)	(271.5)	(368.3)
Less: Comprehensive income attributable to noncontrolling interests	1.6	7.0	8.1	7.8
Comprehensive (loss) income attributable to common stockholders	(358.2)	(12.0)	(279.6)	(376.1)
Parent Company [Member]
Total revenues	0	0	0	0
Operating costs and expenses (exclusive of items shown separately below)	(6.7)	(14.4)	7.2	(168.9)
Depreciation, depletion and amortization	0	0	0	0
Asset retirement obligation expenses	0	0	0	0
Selling and administrative expenses	12.0	11.2	36.6	39.5
Other operating (income) loss:
Net gain on disposal or exchange of assets	0	0	0	0
Asset impairment				21.5
Loss (income) from equity affiliates and investment in subsidiaries	80.9	(98.0)	45.7	(192.1)
Interest expense	106.0	113.0	318.9	316.2
Interest income	0	(0.1)	(0.2)	(68.3)
Unrealized loss (gain) on derivatives		0		0
(Loss) income from continuing operations before income taxes	(192.2)	(11.7)	(408.2)	52.1
Income tax provision (benefit)	(41.1)	10.0	(134.1)	0.5
(Loss) income from continuing operations, net of income taxes	(151.1)	(21.7)	(274.1)	51.6
Income (loss) from discontinued operations, net of income taxes	0.5	(4.4)	1.7	(10.8)
Net (loss) income	(150.6)	(26.1)	(272.4)	40.8
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net (loss) income attributable to common stockholders	(150.6)	(26.1)	(272.4)	40.8
Other comprehensive (loss) income, net of income taxes	(207.6)	14.1	(7.2)	(416.9)
Comprehensive (loss) income	(358.2)	(12.0)	(279.6)	(376.1)
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive (loss) income attributable to common stockholders	(358.2)	(12.0)	(279.6)	(376.1)
Guarantor Subsidiaries [Member]
Total revenues	1,008.1	1,005.8	2,989.5	2,992.9
Operating costs and expenses (exclusive of items shown separately below)	758.2	755.6	2,226.2	2,279.5
Depreciation, depletion and amortization	77.0	83.0	230.4	248.1
Asset retirement obligation expenses	6.5	4.8	22.1	26.6
Selling and administrative expenses	36.4	38.5	120.5	125.7
Other operating (income) loss:
Net gain on disposal or exchange of assets	(4.4)	(4.0)	(16.3)	(49.8)
Asset impairment				0
Loss (income) from equity affiliates and investment in subsidiaries	3.6	2.0	6.3	10.4
Interest expense	1.7	88.2	5.0	99.2
Interest income	(2.8)	(98.8)	(7.3)	(138.5)
Unrealized loss (gain) on derivatives		(19.7)		441.9
(Loss) income from continuing operations before income taxes	131.9	156.2	402.6	(50.2)
Income tax provision (benefit)	57.0	(32.2)	122.8	(117.4)
(Loss) income from continuing operations, net of income taxes	74.9	188.4	279.8	67.2
Income (loss) from discontinued operations, net of income taxes	(0.1)	(1.8)	(1.3)	(4.3)
Net (loss) income	74.8	186.6	278.5	62.9
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net (loss) income attributable to common stockholders	74.8	186.6	278.5	62.9
Other comprehensive (loss) income, net of income taxes	2.7	14.2	5.1	42.7
Comprehensive (loss) income	77.5	200.8	283.6	105.6
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive (loss) income attributable to common stockholders	77.5	200.8	283.6	105.6
Non-Guarantor Subsidiaries [Member]
Total revenues	731.1	823.8	2,177.3	2,438.8
Operating costs and expenses (exclusive of items shown separately below)	718.1	722.9	2,141.4	2,308.9
Depreciation, depletion and amortization	86.6	103.4	253.5	294.7
Asset retirement obligation expenses	8.5	8.6	24.4	24.1
Selling and administrative expenses	4.5	5.3	14.5	18.9
Other operating (income) loss:
Net gain on disposal or exchange of assets	(9.5)	(0.1)	(9.6)	(0.1)
Asset impairment				0
Loss (income) from equity affiliates and investment in subsidiaries	12.2	0.6	37.7	25.2
Interest expense	171.2	22.6	174.3	142.8
Interest income	(165.3)	(18.1)	(179.4)	(39.5)
Unrealized loss (gain) on derivatives		19.7		(441.9)
(Loss) income from continuing operations before income taxes	(95.2)	(41.1)	(279.5)	105.7
Income tax provision (benefit)	63.5	3.6	42.2	(82.7)
(Loss) income from continuing operations, net of income taxes	(158.7)	(44.7)	(321.7)	188.4
Income (loss) from discontinued operations, net of income taxes	4.6	(36.9)	5.6	(51.4)
Net (loss) income	(154.1)	(81.6)	(316.1)	137.0
Less: Net income attributable to noncontrolling interests	1.6	7.0	8.1	7.8
Net (loss) income attributable to common stockholders	(155.7)	(88.6)	(324.2)	129.2
Other comprehensive (loss) income, net of income taxes	(6.7)	(36.4)	(22.6)	(100.5)
Comprehensive (loss) income	(160.8)	(118.0)	(338.7)	36.5
Less: Comprehensive income attributable to noncontrolling interests	1.6	7.0	8.1	7.8
Comprehensive (loss) income attributable to common stockholders	(162.4)	(125.0)	(346.8)	28.7
Eliminations [Member]
Total revenues	(16.3)	(32.0)	(59.1)	(160.8)
Operating costs and expenses (exclusive of items shown separately below)	(16.3)	(32.0)	(59.1)	(160.8)
Depreciation, depletion and amortization	0	0	0	0
Asset retirement obligation expenses	0	0	0	0
Selling and administrative expenses	0	0	0	0
Other operating (income) loss:
Net gain on disposal or exchange of assets	0	0	0	0
Asset impairment				0
Loss (income) from equity affiliates and investment in subsidiaries	(80.9)	98.0	(45.7)	192.1
Interest expense	(164.4)	(112.8)	(175.2)	(235.1)
Interest income	164.4	112.8	175.2	235.1
Unrealized loss (gain) on derivatives		0		0
(Loss) income from continuing operations before income taxes	80.9	(98.0)	45.7	(192.1)
Income tax provision (benefit)	0	0	0	0
(Loss) income from continuing operations, net of income taxes	80.9	(98.0)	45.7	(192.1)
Income (loss) from discontinued operations, net of income taxes	0	0	0	0
Net (loss) income	80.9	(98.0)	45.7	(192.1)
Less: Net income attributable to noncontrolling interests	0	0	0	0
Net (loss) income attributable to common stockholders	80.9	(98.0)	45.7	(192.1)
Other comprehensive (loss) income, net of income taxes	4.0	22.2	17.5	57.8
Comprehensive (loss) income	84.9	(75.8)	63.2	(134.3)
Less: Comprehensive income attributable to noncontrolling interests	0	0	0	0
Comprehensive (loss) income attributable to common stockholders	$ 84.9	$ (75.8)	$ 63.2	$ (134.3)