Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2016

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock option activity [Text Block]

	Shares (thousands)		Weighted average exercise price		Weighted average remaining contractual life (in years)	Aggregate intrinsic value (in millions)
Outstanding at January 1, 2014	1,997		$	15.82	2.6	$	80.0
Exercised	(283	)	$	14.04		$	13.8
Outstanding at December 31, 2014	1,714		$	16.11	1.7	$	66.5
Exercised	(440	)	$	14.76		$	19.2
Forfeited	(7	)	$	14.52
Outstanding at December 31, 2015	1,267		$	16.59	0.9	$	33.7
Exercised	(794	)	$	16.07		$	14.4
Outstanding at December 31, 2016	473		$	17.47	0.1	$	10.4
Options exercisable at December 31, 2016	473		$	17.47	0.1	$	10.4

Proceeds from stock option exercises [Text Block]

	Year Ended December 31,
(millions of dollars)	2016		2015		2014
Proceeds from stock options exercised — gross	$	12.7	$	6.5	$	4.0
Tax benefit	0.3		10.3		12.9
Proceeds from stock options exercised, net of tax	$	13.0	$	16.8	$	16.9

Restricted stock compensation expense [Text Block]

	Year Ended December 31,
(millions of dollars, except per share data)	2016		2015		2014
Restricted stock compensation expense	$	26.7	$	28.0	$	20.7
Restricted stock compensation expense, net of tax	$	19.5	$	20.4	$	15.1

Status of nonvested restricted stock [Text Block]

	Shares subject to restriction (thousands)		Weighted average price
Nonvested at January 1, 2014	1,411		$	37.86
Granted	447		$	54.36
Vested	(530	)	$	37.42
Forfeited	(62	)	$	41.14
Nonvested at December 31, 2014	1,266		$	43.57
Granted	687		$	58.45
Vested	(588	)	$	39.14
Forfeited	(39	)	$	50.85
Nonvested at December 31, 2015	1,326		$	53.18
Granted	724		$	30.07
Vested	(551	)	$	47.55
Forfeited	(70	)	$	43.05
Nonvested at December 31, 2016	1,429		$	44.12

Amounts expensed under plan and share issuances [Text Block]

	Year Ended December 31,
(millions of dollars, except share data)	2016		2015		2014
Expense	$	9.6	$	12.2	$	11.4
Number of shares	—		—		—