Pension plans 4 (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
General insurance account [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the beginning of the year	$ 17.6	$ 19.0
Actual return on plan assets	(0.8)	1.0
Purchases, sales and settlments, net	(0.2)	(3.2)
Defined Benefit Plan, Divestitures, Plan Assets	(9.9)
Foreign currency exchange rates	(1.2)	0.8
Fair value of plan assets at the end of the year	5.5	17.6
U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the beginning of the year	627.2	555.3
Actual return on plan assets	88.6	65.2
Defined Benefit Plan, Divestitures, Plan Assets	0	0
Foreign currency exchange rates		0
Fair value of plan assets at the end of the year	685.7	627.2
U.S. Pension Plans [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	169.7	213.0
U.S. Pension Plans [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	516.0	414.2
U.S. Pension Plans [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | Cash and cash equivalents [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	12.8	5.9
U.S. Pension Plans [Member] | Cash and cash equivalents [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	6.7	9.8
U.S. Pension Plans [Member] | Cash and cash equivalents [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | Corporate debt securities [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | Corporate debt securities [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	243.6	199.2
U.S. Pension Plans [Member] | Corporate debt securities [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | U.S. government debt securities [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	1.1	2.7
U.S. Pension Plans [Member] | U.S. government debt securities [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | U.S. government debt securities [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | State and municipal debt securities [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | State and municipal debt securities [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	48.6	45.6
U.S. Pension Plans [Member] | State and municipal debt securities [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | Corporate common stock [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	144.7	194.2
U.S. Pension Plans [Member] | Corporate common stock [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	15.6	17.5
U.S. Pension Plans [Member] | Corporate common stock [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | Registered investment company funds [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	11.1	10.2
U.S. Pension Plans [Member] | Registered investment company funds [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	151.1	133.3
U.S. Pension Plans [Member] | Registered investment company funds [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | Common trust funds [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | Common trust funds [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	50.4	8.8
U.S. Pension Plans [Member] | Common trust funds [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | General insurance account [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | General insurance account [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
U.S. Pension Plans [Member] | General insurance account [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the beginning of the year	67.2	63.3
Actual return on plan assets	4.0	5.5
Defined Benefit Plan, Divestitures, Plan Assets	(9.9)	0
Foreign currency exchange rates	(4.6)	1.5
Fair value of plan assets at the end of the year	57.2	67.2
Non-U.S. Pension Plans [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	46.7	44.8
Non-U.S. Pension Plans [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	5.0	4.8
Non-U.S. Pension Plans [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	5.5	17.6
Non-U.S. Pension Plans [Member] | Cash and cash equivalents [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Cash and cash equivalents [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Cash and cash equivalents [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Corporate debt securities [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Corporate debt securities [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Corporate debt securities [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | U.S. government debt securities [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | U.S. government debt securities [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | U.S. government debt securities [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | State and municipal debt securities [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | State and municipal debt securities [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | State and municipal debt securities [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Corporate common stock [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Corporate common stock [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Corporate common stock [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Registered investment company funds [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	46.7	44.8
Non-U.S. Pension Plans [Member] | Registered investment company funds [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Registered investment company funds [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Common trust funds [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | Common trust funds [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	5.0	4.8
Non-U.S. Pension Plans [Member] | Common trust funds [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | General insurance account [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | General insurance account [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	0	0
Non-U.S. Pension Plans [Member] | General insurance account [Member] | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	$ 5.5	$ 17.6