Financial Information for Guarantor Subsidiaries and Non-Guarantor Subsidiaries - Supplemental Condensed Consolidating Statement of Operations and Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended								12 Months Ended
	Feb. 28, 2018	Aug. 31, 2017	Feb. 28, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Total revenue				$ 885.7	$ 821.0	$ 844.7	$ 811.8	$ 823.0	$ 768.9	$ 766.3	$ 725.4	$ 3,363.2	$ 3,083.6	$ 2,883.4
Cost of revenues				341.4	301.3	315.9	296.7	314.9	290.8	278.9	280.0	1,255.3	1,164.6	1,106.3
Selling, general and administrative				181.7	169.7	173.9	171.6	167.7	158.8	145.9	140.7	696.9	613.1	577.0
Research and development				49.8	49.5	49.2	53.8	45.8	47.8	48.1	42.4	202.3	184.1	204.8
Depreciation, amortization and impairments				162.6	166.3	172.7	188.1	169.6	173.1	175.0	165.1	689.7	682.8	738.7
Goodwill impairment												0.0	0.0	69.0
Restructuring and other				(171.0)	338.7	33.5	52.2	27.8	7.8	1.1	9.2	253.4	45.9	57.0
Operating income (loss)				321.2	(204.5)	99.5	49.4	97.2	90.6	117.3	88.0	265.6	393.1	130.6
Interest expense												(597.2)	(609.7)	(661.4)
(Loss) gain on debt financing transactions	$ (93.2)	$ (8.4)	$ (29.7)									(93.2)	(38.1)	25.2
Gain on remeasurement of debt				14.0	(4.0)	34.5	(1.1)					43.4	0.0	0.0
Other income (expense), net												42.1	26.9	26.9
Net (loss) income before income taxes												(339.3)	(227.8)	(478.7)
Equity in (loss) income of subsidiaries												0.0	0.0	0.0
Income tax (expense) benefit												(13.1)	(14.5)	125.0
Net (loss) income				$ 206.8	$ (351.6)	$ (5.8)	$ (201.8)	$ (43.1)	$ (59.3)	$ (39.1)	$ (100.8)	(352.4)	(242.3)	(353.7)
Other comprehensive (loss) income												(99.8)	133.9	(111.4)
Comprehensive (loss) income												(452.2)	(108.4)	(465.1)
Reportable Legal Entities | Parent Company
Condensed Financial Statements, Captions [Line Items]
Total revenue												0.0	0.0	0.0
Cost of revenues												0.0	0.0	0.0
Selling, general and administrative												154.4	127.1	121.0
Research and development												0.0	2.1	6.1
Depreciation, amortization and impairments												44.2	71.6	53.5
Goodwill impairment														0.0
Restructuring and other												194.7	29.7	32.6
Operating income (loss)												(393.3)	(230.5)	(213.2)
Interest expense												0.0	(4.6)	(21.0)
(Loss) gain on debt financing transactions												0.0	(1.1)	0.0
Gain on remeasurement of debt												0.0
Other income (expense), net												335.7	87.7	64.0
Net (loss) income before income taxes												(57.6)	(148.5)	(170.2)
Equity in (loss) income of subsidiaries												(218.5)	(45.4)	(180.1)
Income tax (expense) benefit												(76.3)	(48.4)	(3.4)
Net (loss) income												(352.4)	(242.3)	(353.7)
Other comprehensive (loss) income												(99.8)	133.9	(111.4)
Comprehensive (loss) income												(452.2)	(108.4)	(465.1)
Reportable Legal Entities | Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Total revenue												1,654.0	1,683.9	1,583.5
Cost of revenues												490.3	511.0	480.9
Selling, general and administrative												227.0	244.4	213.8
Research and development												87.2	101.3	145.2
Depreciation, amortization and impairments												439.4	462.7	534.6
Goodwill impairment														0.0
Restructuring and other												9.2	7.3	11.7
Operating income (loss)												400.9	357.2	197.3
Interest expense												0.0	0.0	0.0
(Loss) gain on debt financing transactions												0.0	0.0	0.0
Gain on remeasurement of debt												0.0
Other income (expense), net												(744.8)	(184.7)	(227.3)
Net (loss) income before income taxes												(343.9)	172.5	(30.0)
Equity in (loss) income of subsidiaries												(28.2)	21.9	61.1
Income tax (expense) benefit												82.3	(85.6)	15.9
Net (loss) income												(289.8)	108.8	47.0
Other comprehensive (loss) income												(66.3)	65.8	(43.1)
Comprehensive (loss) income												(356.1)	174.6	3.9
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Total revenue												1,540.3	1,223.3	1,148.6
Cost of revenues												721.2	629.1	553.8
Selling, general and administrative												325.5	250.2	235.9
Research and development												112.4	74.2	42.8
Depreciation, amortization and impairments												188.3	128.0	116.0
Goodwill impairment														69.0
Restructuring and other												50.6	3.8	8.1
Operating income (loss)												142.3	138.0	123.0
Interest expense												(0.5)	(1.2)	(0.2)
(Loss) gain on debt financing transactions												0.0	0.0	0.0
Gain on remeasurement of debt												0.0
Other income (expense), net												(83.7)	(26.5)	(4.2)
Net (loss) income before income taxes												58.1	110.3	118.6
Equity in (loss) income of subsidiaries												0.0	0.0	0.0
Income tax (expense) benefit												(19.6)	(38.4)	(25.7)
Net (loss) income												38.5	71.9	92.9
Other comprehensive (loss) income												(113.8)	128.7	(135.1)
Comprehensive (loss) income												(75.3)	200.6	(42.2)
Reportable Legal Entities | SGI
Condensed Financial Statements, Captions [Line Items]
Total revenue												547.1	498.1	469.5
Cost of revenues												360.9	341.9	328.6
Selling, general and administrative												42.4	41.3	46.9
Research and development												2.7	6.5	10.7
Depreciation, amortization and impairments												32.6	31.3	40.9
Goodwill impairment														0.0
Restructuring and other												(1.1)	5.1	4.6
Operating income (loss)												109.6	72.0	37.8
Interest expense												(596.7)	(603.9)	(640.2)
(Loss) gain on debt financing transactions												(93.2)	(37.0)	25.2
Gain on remeasurement of debt												43.4
Other income (expense), net												534.9	150.4	194.4
Net (loss) income before income taxes												(2.0)	(418.5)	(382.8)
Equity in (loss) income of subsidiaries												43.6	67.6	48.5
Income tax (expense) benefit												0.5	157.9	138.2
Net (loss) income												42.1	(193.0)	(196.1)
Other comprehensive (loss) income												30.0	10.3	(1.7)
Comprehensive (loss) income												72.1	(182.7)	(197.8)
Eliminating Entries
Condensed Financial Statements, Captions [Line Items]
Total revenue												(378.2)	(321.7)	(318.2)
Cost of revenues												(317.1)	(317.4)	(257.0)
Selling, general and administrative												(52.4)	(49.9)	(40.6)
Research and development												0.0	0.0	0.0
Depreciation, amortization and impairments												(14.8)	(10.8)	(6.3)
Goodwill impairment														0.0
Restructuring and other												0.0	0.0	0.0
Operating income (loss)												6.1	56.4	(14.3)
Interest expense												0.0	0.0	0.0
(Loss) gain on debt financing transactions												0.0	0.0	0.0
Gain on remeasurement of debt												0.0
Other income (expense), net												0.0	0.0	0.0
Net (loss) income before income taxes												6.1	56.4	(14.3)
Equity in (loss) income of subsidiaries												203.1	(44.1)	70.5
Income tax (expense) benefit												0.0	0.0	0.0
Net (loss) income												209.2	12.3	56.2
Other comprehensive (loss) income												150.1	(204.8)	179.9
Comprehensive (loss) income												$ 359.3	$ (192.5)	$ 236.1