Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2015

Asset Retirement Obligation [Abstract]

Change in Asset Retirement Obligations

The following table shows changes to our AROs:

(in millions)	2015			2014			2013
Balance as of January 1	$	40.5		$	39.4		$	41.5
Accretion	2.3			2.2			2.2
Additions	15.9		*	—			—
Liabilities settled	—			(1.1		)	(4.3		)
Balance as of December 31	$	58.7		$	40.5		$	39.4

* An ARO was recorded during 2015 for the fly-ash landfills located at our generation facilities.