Postretirement Health Care and Life Insurance Benefits (Details 2) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in Postretirement Obligations		$ 18.7	$ 9.6	$ 17.0
Reconciled amount of plans funded status
Other		3.7	0.0
Postretirement Health Care and Life Insurance Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in Postretirement Obligations		27.6
Reconciled amount of plans funded status
Projected benefit obligation at beginning of period		839.1	735.4
Service cost		11.2	12.2	15.8
Interest cost		33.8	36.4	41.8
Participant contributions		1.7	2.2
Plan changes	[1]	(16.6)	(18.0)
Benefits paid		(46.5)	(46.5)
Actuarial (gain) loss	[2]	(35.1)	115.8
Settlement charges related to the Patriot bankruptcy	[3]	(15.2)	0.0
Special termination benefits	[4]	0.0	1.6	0.9
Projected benefit obligation at end of period		776.1	839.1	735.4
Fair value of plan assets at beginning of period		0.0	0.0
Employer contributions		44.8	44.3
Participant contributions		1.7	2.2
Benefits paid and administrative fees (net of Medicare Part D reimbursements)		(46.5)	(46.5)
Fair value of plan assets at end of period		0.0	0.0	$ 0.0
Funded status at end of year		(776.1)	(839.1)
Less current portion (included in Accounts payable and accrued expenses)		53.2	57.2
Noncurrent obligation (included in Accrued postretirement benefit costs)		(722.9)	$ (781.9)
Demographic Assumptions Change [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in Postretirement Obligations		63.0
Postretirement plan change [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase (Decrease) in Postretirement Obligations		$ (45.4)

[1] Refer to Note 25. "Matters Related to the Bankruptcy of Patriot Coal Corporation" herein for additional details related to the reduction in the benefit obligation for 2015. In 2014, the Company made various plan changes that became effective January 1, 2015 for certain plan participants designed to bring consistency amongst the various retiree medical programs which resulted in a $45.4 million reduction to the benefit obligation. In addition, the Company made a plan change effective April 1, 2014 for certain plan participants' benefits no longer funded through a Medicare Advantage Program which resulted in a $27.6 million increase to the benefit obligation. The plan changes will not affect participant benefits.

[2] In 2014, the Company reviewed its demographic assumptions (including mortality, retirements and terminations) in conjunction with the recently-issued mortality tables published by the Society of Actuaries, to select assumptions that are aligned with the Company’s experience. The updated demographic assumptions increased the December 31, 2014 benefit obligation by approximately $63 million

[3] Refer to Note 25. "Matters Related to the Bankruptcy of Patriot Coal Corporation" herein for additional details related to this transaction.

[4] Reflected in "Restructuring and pension settlement charges" in the consolidated statement of operations for the year ended December 31, 2014.