Accumulated other comprehensive income (loss) - Amounts in OCI (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	$ (28.7)			$ (27.9)			$ (42.1)	$ (54.9)
Amounts Arising During the Current Period, Income Tax	(10.7)			(5.6)			(8.1)	(1.8)
Amounts Reclassified to Net Income (Loss), Pretax	8.2			10.9			36.3	52.3
Amounts Reclassified to Net Income (Loss), Income Tax	(1.9)			(1.8)			(9.4)	(13.3)
Other comprehensive loss	(33.1)	$ (39.6)	$ 49.4	(24.4)	$ 49.5	$ (42.8)	(23.3)	(17.7)
Cost of revenues	880.7			837.6			2,587.9	2,415.6
Selling, general and administrative expenses	180.8			161.9			519.9	472.0
Interest and other income (expense)	6.3			(0.7)			8.4	(1.6)
Other operating income (expense)	(15.7)			(1.8)			(18.4)	(5.2)
Interest expense	34.7			27.6			95.0	83.0
Benefit plan adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(0.6)			6.0			0.4	(12.3)
Amounts Arising During the Current Period, Income Tax	0.2			(1.1)			0.3	3.9
Amounts Reclassified to Net Income (Loss), Pretax	9.4			15.3			29.1	46.5
Amounts Reclassified to Net Income (Loss), Income Tax	(2.2)			(3.6)			(6.9)	(11.9)
Other comprehensive loss	6.8			16.6			22.9	26.2
Foreign currency translation adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(36.8)			(38.4)			(57.8)	(43.9)
Amounts Arising During the Current Period, Income Tax	(7.3)			(2.3)			(2.9)	(4.3)
Amounts Reclassified to Net Income (Loss), Pretax	(1.4)			(1.5)			(4.4)	(2.6)
Amounts Reclassified to Net Income (Loss), Income Tax	0.3			0.4			1.0	0.6
Other comprehensive loss	(45.2)			(41.8)			(64.1)	(50.2)
Unrealized losses on available-for-sale securities
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	0.7						0.0
Amounts Arising During the Current Period, Income Tax	(0.9)						(1.0)
Amounts Reclassified to Net Income (Loss), Pretax	0.0						0.0
Amounts Reclassified to Net Income (Loss), Income Tax	0.0						0.0
Other comprehensive loss	(0.2)						(1.0)
Gains (losses) on cash flow hedges
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	12.0			5.8			25.8	4.4
Amounts Arising During the Current Period, Income Tax	(2.7)			(2.2)			(4.5)	(1.4)
Amounts Reclassified to Net Income (Loss), Pretax	0.2			(2.9)			11.6	8.4
Amounts Reclassified to Net Income (Loss), Income Tax	0.0			1.4			(3.5)	(2.0)
Other comprehensive loss	9.5			2.1			29.4	9.4
Gains (losses) on cash flow hedges | Reclassification out of accumulated other comprehensive income
Other Comprehensive Income Loss [Line Items]
Other operating income (expense)	(6.2)			5.6			0.3	0.0
Interest expense	0.5			2.7			5.4	8.4
AOCI Attributable to Parent
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(24.7)			(26.6)			(31.6)	(51.8)
Amounts Arising During the Current Period, Income Tax	(10.7)			(5.6)			(8.1)	(1.8)
Amounts Reclassified to Net Income (Loss), Pretax	8.2			10.9			36.3	52.3
Amounts Reclassified to Net Income (Loss), Income Tax	(1.9)			(1.8)			(9.4)	(13.3)
Other comprehensive loss	(29.1)	$ (34.6)	$ 50.9	(23.1)	$ 49.2	$ (40.7)	(12.8)	(14.6)
Benefit plan adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax								(0.3)
Other comprehensive loss								(0.3)
Foreign currency translation adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(4.0)			(1.3)			(10.5)	(2.8)
Amounts Arising During the Current Period, Income Tax	0.0			0.0			0.0	0.0
Amounts Reclassified to Net Income (Loss), Pretax	0.0			0.0			0.0	0.0
Amounts Reclassified to Net Income (Loss), Income Tax	0.0			0.0			0.0	0.0
Other comprehensive loss	(4.0)			(1.3)			(10.5)	(2.8)
AOCI Attributable to Noncontrolling Interest
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(4.0)			(1.3)			(10.5)	(3.1)
Amounts Arising During the Current Period, Income Tax	0.0			0.0			0.0	0.0
Amounts Reclassified to Net Income (Loss), Pretax	0.0			0.0			0.0	0.0
Amounts Reclassified to Net Income (Loss), Income Tax	0.0			0.0			0.0	0.0
Other comprehensive loss	(4.0)			(1.3)			(10.5)	(3.1)
Benefit plan adjustments(a)
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(0.6)			6.0			0.4	(12.6)
Amounts Arising During the Current Period, Income Tax	0.2			(1.1)			0.3	3.9
Amounts Reclassified to Net Income (Loss), Pretax	9.4			15.3			29.1	46.5
Amounts Reclassified to Net Income (Loss), Income Tax	(2.2)			(3.6)			(6.9)	(11.9)
Other comprehensive loss	6.8			16.6			22.9	25.9
Benefit plan adjustments(a) | Reclassification out of accumulated other comprehensive income
Other Comprehensive Income Loss [Line Items]
Cost of revenues	1.5			1.8			4.8	5.5
Selling, general and administrative expenses	0.5			0.3			1.4	1.4
Interest and other income (expense)	3.1			9.3			11.1	27.6
Foreign currency translation adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(40.8)			(39.7)			(68.3)	(46.7)
Amounts Arising During the Current Period, Income Tax	(7.3)			(2.3)			(2.9)	(4.3)
Amounts Reclassified to Net Income (Loss), Pretax	(1.4)			(1.5)			(4.4)	(2.6)
Amounts Reclassified to Net Income (Loss), Income Tax	0.3			0.4			1.0	0.6
Other comprehensive loss	(49.2)			(43.1)			(74.6)	(53.0)
Unrealized losses on available-for-sale securities(c)
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	0.7						0.0
Amounts Arising During the Current Period, Income Tax	(0.9)						(1.0)
Amounts Reclassified to Net Income (Loss), Pretax	0.0						0.0
Amounts Reclassified to Net Income (Loss), Income Tax	0.0						0.0
Other comprehensive loss	(0.2)						(1.0)
Gains (losses) on cash flow hedges(d)
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	12.0			5.8			25.8	4.4
Amounts Arising During the Current Period, Income Tax	(2.7)			(2.2)			(4.5)	(1.4)
Amounts Reclassified to Net Income (Loss), Pretax	0.2			(2.9)			11.6	8.4
Amounts Reclassified to Net Income (Loss), Income Tax	0.0			1.4			(3.5)	(2.0)
Other comprehensive loss	$ 9.5			$ 2.1			$ 29.4	$ 9.4