Accumulated Other Comprehensive Income - Amounts in OCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	$ (74.9)	$ (68.0)	$ (163.7)
Amounts Arising During the Current Period, Income Tax	19.5	16.7	20.5
Amounts Reclassified to Net Income (Loss), Pretax	54.3	53.1	59.6
Amounts Reclassified to Net Income (Loss), income Tax	(17.7)	(17.6)	(19.8)
Other comprehensive loss	(18.8)	(15.8)	(103.4)
Cost of revenues	2,608.2	2,391.7	2,443.7
Selling, general and administrative expenses	468.2	424.3	451.9
Interest and other income (expense)	(60.2)	(39.1)	(36.4)
Other operating expense	(3.3)	20.1	69.4
Benefit plan adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(99.3)	(39.5)	(57.1)
Amounts Arising During the Current Period, Income Tax	21.2	16.7	20.4
Amounts Reclassified to Net Income (Loss), Pretax	54.9	51.3	58.1
Amounts Reclassified to Net Income (Loss), income Tax	(18.2)	(17.6)	(20.2)
Other comprehensive loss	(41.4)	10.9	1.2
Foreign currency translation adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	22.7	(26.6)	(106.2)
Amounts Arising During the Current Period, Income Tax	(1.0)	0.2	0.3
Amounts Reclassified to Net Income (Loss), Pretax	0.0	(0.1)	5.7
Amounts Reclassified to Net Income (Loss), income Tax	0.0	0.0	0.0
Other comprehensive loss	21.7	(26.5)	(100.2)
Unrealized gains (losses) on available-for-sale securities
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	1.7	0.4	0.6
Amounts Arising During the Current Period, Income Tax	(0.6)	(0.2)	(0.2)
Amounts Reclassified to Net Income (Loss), Pretax	(1.5)	(0.5)	(1.1)
Amounts Reclassified to Net Income (Loss), income Tax	0.5	0.2	0.4
Other comprehensive loss	0.1	(0.1)	(0.3)
Gains (losses) on cash flow hedges
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(0.1)	(1.2)	3.3
Amounts Arising During the Current Period, Income Tax	(0.1)	0.0	0.0
Amounts Reclassified to Net Income (Loss), Pretax	0.2	2.0	(3.6)
Amounts Reclassified to Net Income (Loss), income Tax	0.0	(0.2)	0.0
Other comprehensive loss	0.0	0.6	(0.3)
Gains (losses) on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income
Other Comprehensive Income Loss [Line Items]
Interest and other income (expense)	(0.1)	(0.3)	(0.5)
Other operating expense	0.1	1.3	(4.1)
AOCI Attributable to Parent
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(75.0)	(66.9)	(159.4)
Amounts Arising During the Current Period, Income Tax	19.5	16.7	20.5
Amounts Reclassified to Net Income (Loss), Pretax	53.6	52.7	59.1
Amounts Reclassified to Net Income (Loss), income Tax	(17.7)	(17.6)	(19.8)
Other comprehensive loss	(19.6)	(15.1)	(99.6)
Benefit plan adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(0.8)	(1.5)	(0.7)
Amounts Arising During the Current Period, Income Tax	0.0	0.0	0.0
Amounts Reclassified to Net Income (Loss), Pretax	0.7	0.4	0.5
Amounts Reclassified to Net Income (Loss), income Tax	0.0	0.0	0.0
Other comprehensive loss	(0.1)	(1.1)	(0.2)
Foreign currency translation adjustments
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	0.9	0.4	(3.6)
Amounts Arising During the Current Period, Income Tax	0.0	0.0	0.0
Amounts Reclassified to Net Income (Loss), Pretax	0.0	0.0	0.0
Amounts Reclassified to Net Income (Loss), income Tax	0.0	0.0	0.0
Other comprehensive loss	0.9	0.4	(3.6)
AOCI Attributable to Noncontrolling Interest
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	0.1	(1.1)	(4.3)
Amounts Arising During the Current Period, Income Tax	0.0	0.0	0.0
Amounts Reclassified to Net Income (Loss), Pretax	0.7	0.4	0.5
Amounts Reclassified to Net Income (Loss), income Tax	0.0	0.0	0.0
Other comprehensive loss	0.8	(0.7)	(3.8)
Benefit plan adjustments(a)
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(100.1)	(41.0)	(57.8)
Amounts Arising During the Current Period, Income Tax	21.2	16.7	20.4
Amounts Reclassified to Net Income (Loss), Pretax	55.6	51.7	58.6
Amounts Reclassified to Net Income (Loss), income Tax	(18.2)	(17.6)	(20.2)
Other comprehensive loss	(41.5)	9.8	1.0
Foreign currency translation adjustments(b)
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	23.6	(26.2)	(109.8)
Amounts Arising During the Current Period, Income Tax	(1.0)	0.2	0.3
Amounts Reclassified to Net Income (Loss), Pretax	0.0	(0.1)	5.7
Amounts Reclassified to Net Income (Loss), income Tax	0.0	0.0	0.0
Other comprehensive loss	22.6	(26.1)	(103.8)
Unrealized gains (losses) on available-for-sale securities(c)
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	1.7	0.4	0.6
Amounts Arising During the Current Period, Income Tax	(0.6)	(0.2)	(0.2)
Amounts Reclassified to Net Income (Loss), Pretax	(1.5)	(0.5)	(1.1)
Amounts Reclassified to Net Income (Loss), income Tax	0.5	0.2	0.4
Other comprehensive loss	0.1	(0.1)	(0.3)
Gains (losses) on cash flow hedges(d)
Other Comprehensive Income Loss [Line Items]
Amounts Arising During the Current Period, Pretax	(0.1)	(1.2)	3.3
Amounts Arising During the Current Period, Income Tax	(0.1)	0.0	0.0
Amounts Reclassified to Net Income (Loss), Pretax	0.2	2.0	(3.6)
Amounts Reclassified to Net Income (Loss), income Tax	0.0	(0.2)	0.0
Other comprehensive loss	0.0	0.6	(0.3)
Benefit Plan Adjustments
Other Comprehensive Income Loss [Line Items]
Other comprehensive loss	(41.4)	10.9	1.2
Benefit Plan Adjustments | Reclassification out of Accumulated Other Comprehensive Income
Other Comprehensive Income Loss [Line Items]
Cost of revenues	9.0	8.9	8.2
Selling, general and administrative expenses	2.4	1.6	2.4
Interest and other income (expense)	$ 47.8	$ 40.3	$ 39.8