ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Other operating income

Included in other operating income were the following:

	Years Ended December 31,
	2017		2016			2015
	($ in millions)
Gains (losses) on disposition of property, plant and equipment, net	$	3.1	$	(0.7	)	$	(0.6	)
Gains on insurance recoveries	—		11.0			46.0
Other	0.2		0.3			0.3
Other operating income	$	3.3	$	10.6		$	45.7

Asset retirement obligation activity

The activities of our asset retirement obligations were as follows:

	December 31,
	2017			2016
	($ in millions)
Beginning balance	$	55.4		$	53.5
Accretion	3.0			3.1
Spending	(8.8		)	(8.8		)
Currency translation adjustments	0.2			0.2
Adjustments	4.5			7.4
Ending balance	$	54.3		$	55.4

Schedule of assumptions for the Black-Scholes option pricing model

The fair value of each option granted, which typically vests ratably over three years, but not less than one year, was estimated on the date of grant, using the Black-Scholes option-pricing model with the following assumptions:

	2017			2016			2015
Dividend yield	2.69		%	6.09		%	2.92		%
Risk-free interest rate	2.06		%	1.35		%	1.69		%
Expected volatility	34		%	32		%	34		%
Expected life (years)	6.0			6.0			6.0
Weighted-average grant fair value (per option)	$	7.78		$	1.90		$	6.80
Weighted-average exercise price	$	29.82		$	13.14		$	27.40
Shares granted	1,621,000			1,670,400			776,750