Pension plans 4 (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Corporate debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the beginning of the year	$ 2.7	$ 0.6
Actual return on plan assets	(0.1)	0.9
Purchases, sales and settlments, net	(2.5)	0.7
Transfer into (out of) Level 3	(0.1)	0.5
Foreign currency exchange rates	0	0
Fair value of plan assets at the end of the year	0	2.7
U.S. government debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the beginning of the year	0	1.0
Actual return on plan assets	0	0
Purchases, sales and settlments, net	0	0
Transfer into (out of) Level 3	0	(1.0)
Foreign currency exchange rates	0	0
Fair value of plan assets at the end of the year	0	0
General insurance account [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the beginning of the year	19.1	18.2
Actual return on plan assets	0.8	1.3
Purchases, sales and settlments, net	(1.2)	0.3
Transfer into (out of) Level 3	0	0
Foreign currency exchange rates	0.3	(0.7)
Fair value of plan assets at the end of the year	19.0	19.1
U.S. Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the beginning of the year	481.4	476.9
Actual return on plan assets	68.6	15.1
Foreign currency exchange rates	0	0
Fair value of plan assets at the end of the year	555.3	481.4
U.S. Pension Plans [Member] | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	293.6	308.8
U.S. Pension Plans [Member] | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at the end of the year	261.6	169.9
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	2.7
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	4.0	1.6
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	10.4	10.2
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	123.1	65.6
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	2.7
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	2.2	18.3
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	40.7
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	19.1	13.0
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	265.0	265.1
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	19.7	19.6
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	22.4	23.8
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	74.5	0
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	14.8	20.8
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	58.7	52.3
Actual return on plan assets	4.3	1.9
Foreign currency exchange rates	2.1	(1.4)
Fair value of plan assets at the end of the year	63.3	58.7
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	39.9	35.5
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	4.4	4.1
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	19.0	19.1
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	39.9	35.5
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	4.4	4.1
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	$ 19.0	$ 19.1