Pension plans 2 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Benefit Obligation and Fair Value of Plan Assets and Reconciliation of Funded Status [Abstract]
Accumulated benefit obligation at the end of the year	$ 802.1	$ 833.1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer contributions	2.9	10.8
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Non-current pension and other post-retirement liability	99.8	102.4
Deferred tax asset	89.0	85.9
Accumulated other comprehensive loss (income)	$ 143.4	$ 140.4	$ 90.7
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plan Assets Percentage	92.00%	92.00%
Defined Benefit Plan, Projected Benefit Obligation Percentage	93.00%	92.00%
U.S. Pension Plans [Member]
Defined Benefit Plan, Change in Benefit Obligation and Fair Value of Plan Assets and Reconciliation of Funded Status [Abstract]
Benefit obligation at the beginning of the year	$ 774.6	$ 641.4
Service cost	6.1	4.9
Interest cost	30.3	30.7
Participant contributions	0.0	0.0
Plan amendments	1.2	0.1
Plan settlements	0.0	0.0
Plan curtailments	0.0	(0.5)
Benefits paid	(34.1)	(36.0)
Actuarial loss	(27.7)	134.0
Transfer in	0.0	0.0
Foreign currency exchange rates	0.0	0.0
Benefit obligation at the end of the year	750.4	774.6	641.4
Accumulated benefit obligation at the end of the year	750.4	774.6
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	685.7	627.2
Actual return on plan assets	(11.6)	88.6
Employer contributions	1.3	5.9
Plan settlements	0.0	0.0
Defined Benefit Plan, Divestitures, Plan Assets	0.0	0.0
Foreign currency exchange rates	0.0	0.0
Fair value of plan assets at the end of the year	641.3	685.7	627.2
Unfunded status at year end:	(109.1)	(88.9)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Prepaid benefit cost, non-current	0.0	0.0
Accrued benefit liability, current	(19.2)	(1.6)
Non-current pension and other post-retirement liability	(89.9)	(87.3)
Subtotal	(109.1)	(88.9)
Deferred tax asset	89.7	85.1
Accumulated other comprehensive loss (income)	142.0	134.7
Net amount related to pension plans	122.6	130.9
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Unrecognized net actuarial losses	227.3	215.7
Unrecognized net prior service costs	4.4	4.1
Unrecognized net transition costs	0.0	0.0
Tax benefit	(89.7)	(85.1)
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Net actuarial losses	14.5
Net prior service costs	0.8
Total	15.3
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	750.4	774.6
Accumulated benefit obligation	750.4	774.6
Fair value of plan assets	641.3	685.7
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	750.4	774.6
Accumulated benefit obligation	750.4	774.6
Fair value of plan assets	641.3	685.7
Non-U.S. Pension Plans [Member]
Defined Benefit Plan, Change in Benefit Obligation and Fair Value of Plan Assets and Reconciliation of Funded Status [Abstract]
Benefit obligation at the beginning of the year	65.9	83.4
Service cost	1.7	2.6
Interest cost	2.3	3.3
Participant contributions	0.2	0.3
Plan amendments	0.0	0.0
Plan settlements	0.0	(0.7)
Plan curtailments	0.0	(0.4)
Benefits paid	(2.2)	(4.0)
Actuarial loss	(5.8)	8.4
Transfer in	0.0	(21.1)
Foreign currency exchange rates	(4.8)	(5.9)
Benefit obligation at the end of the year	57.3	65.9	83.4
Accumulated benefit obligation at the end of the year	51.7	58.5
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at the beginning of the year	57.2	67.2
Actual return on plan assets	1.5	4.0
Employer contributions	1.6	4.9
Plan settlements	0.0	(0.7)
Defined Benefit Plan, Divestitures, Plan Assets	0.0	(9.9)
Foreign currency exchange rates	(4.1)	(4.6)
Fair value of plan assets at the end of the year	54.2	57.2	67.2
Unfunded status at year end:	(3.1)	(8.7)
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]
Prepaid benefit cost, non-current	1.9	0.0
Accrued benefit liability, current	(0.4)	(0.2)
Non-current pension and other post-retirement liability	(4.6)	(8.5)
Subtotal	(3.1)	(8.7)
Deferred tax asset	1.3	2.6
Accumulated other comprehensive loss (income)	4.5	8.4
Net amount related to pension plans	2.7	2.3
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]
Unrecognized net actuarial losses	5.4	10.4
Unrecognized net prior service costs	0.1	0.1
Unrecognized net transition costs	0.3	0.5
Tax benefit	(1.3)	(2.6)
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract]
Net actuarial losses	(0.1)
Net prior service costs	0.0
Total	(0.1)
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	17.2	65.9
Accumulated benefit obligation	14.1	58.5
Fair value of plan assets	12.2	57.2
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]
Projected benefit obligation	11.7	13.7
Accumulated benefit obligation	10.4	11.9
Fair value of plan assets	7.5	8.2
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation and Fair Value of Plan Assets and Reconciliation of Funded Status [Abstract]
Service cost	7.8	7.5	14.0
Interest cost	32.6	$ 34.0	$ 32.5
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 20.6