Basis of Presentation and Significant Accounting Policies - Summary of Impact of Adoption of Topic 842 on Condensed Consolidated Statement of Operations and Condensed Consolidated Balance Sheet (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017
Balance Sheet Classification [Abstract]
Prepaid expenses and other	$ 277.3		$ 277.3		$ 275.6
Current assets held for sale	2,545.7		2,545.7		3,535.2
Total current assets	7,061.7		7,061.7		7,740.3
Total assets	17,666.3		17,666.3		17,722.4
Other accrued liabilities	1,326.2		1,326.2		1,180.7
Current liabilities held for sale	538.0		538.0		734.8
Total current liabilities	3,135.8		3,135.8		3,412.8
Other noncurrent liabilities	1,220.5		1,220.5		1,369.1
Total liabilities	12,661.7		12,661.7		12,469.2
Retained deficit	(2,572.2)		(2,572.2)		(2,511.3)
Stockholders’ equity attributable to parent	4,969.2		4,969.2		5,218.4
Total stockholders’ equity	5,004.6	$ 13,991.2	5,004.6	$ 13,991.2	5,253.2	$ 4,983.1	$ 14,167.3	$ 14,181.3
Total liabilities and stockholders’ equity	17,666.3		17,666.3		17,722.4
Income Statement Classification [Abstract]
Income (loss) from discontinued operations, net of tax	6.8	208.1	(72.6)	316.1
Net income (loss)	$ 89.8	$ 131.7	$ (61.4)	$ 185.0
Basic:
Income (loss) from continuing operations (in USD per share)	$ 0.20	$ (0.16)	$ 0.03	$ (0.27)
Income (loss) from discontinued operations (in USD per share)	0.01	0.43	(0.17)	0.65
Net income (loss) (in USD per share)	0.21	0.27	(0.14)	0.38
Diluted:
Income (loss) from continuing operations (in USD per share)	0.20	(0.16)	0.03	(0.27)
Income (loss) from discontinued operations (in USD per share)	0.01	0.43	(0.17)	0.65
Net income (loss) (in USD per share)	$ 0.21	$ 0.27	$ (0.14)	$ 0.38
Previously Reported
Balance Sheet Classification [Abstract]
Prepaid expenses and other					278.0
Current assets held for sale					3,541.3
Total current assets					7,748.8
Deferred income taxes (noncurrent assets)					165.2
Total assets					17,716.4
Other accrued liabilities					1,182.3
Current liabilities held for sale					650.4
Total current liabilities					3,330.0
Deferred income taxes (liabilities)					1,041.8
Other noncurrent liabilities					1,370.5
Total liabilities					12,438.6
Retained deficit					(2,486.7)
Stockholders’ equity attributable to parent					5,243.0
Total stockholders’ equity					5,277.8
Total liabilities and stockholders’ equity					17,716.4
Income Statement Classification [Abstract]
Income (loss) from discontinued operations, net of tax					(128.3)
Net income (loss)					$ (6,917.9)
Basic:
Income (loss) from continuing operations (in USD per share)					$ (14.33)
Income (loss) from discontinued operations (in USD per share)					(0.27)
Net income (loss) (in USD per share)					(14.60)
Diluted:
Income (loss) from continuing operations (in USD per share)					(14.33)
Income (loss) from discontinued operations (in USD per share)					(0.27)
Net income (loss) (in USD per share)					$ (14.60)
Restatement Adjustment
Balance Sheet Classification [Abstract]
Prepaid expenses and other					$ (2.4)
Current assets held for sale					(6.1)
Total current assets					(8.5)
Deferred income taxes (noncurrent assets)					14.5
Total assets					6.0
Other accrued liabilities					(0.8)
Current liabilities held for sale					100.4
Total current liabilities					99.6
Deferred income taxes (liabilities)					(66.7)
Other noncurrent liabilities					(2.3)
Total liabilities					30.6
Retained deficit					(24.6)
Stockholders’ equity attributable to parent					(24.6)
Total stockholders’ equity					(24.6)
Total liabilities and stockholders’ equity					6.0
Income Statement Classification [Abstract]
Income (loss) from discontinued operations, net of tax					(24.6)
Net income (loss)					$ (24.6)
Basic:
Income (loss) from continuing operations (in USD per share)					$ 0
Income (loss) from discontinued operations (in USD per share)					(0.05)
Net income (loss) (in USD per share)					(0.05)
Diluted:
Income (loss) from continuing operations (in USD per share)					0
Income (loss) from discontinued operations (in USD per share)					(0.05)
Net income (loss) (in USD per share)					$ (0.05)
Reclassification
Balance Sheet Classification [Abstract]
Prepaid expenses and other					$ 0.0
Current assets held for sale					0.0
Total current assets					0.0
Deferred income taxes (noncurrent assets)					0.0
Total assets					0.0
Other accrued liabilities					(0.8)
Current liabilities held for sale					(16.0)
Total current liabilities					(16.8)
Deferred income taxes (liabilities)					15.9
Other noncurrent liabilities					0.9
Total liabilities					0.0
Retained deficit					0.0
Stockholders’ equity attributable to parent					0.0
Total stockholders’ equity					0.0
Total liabilities and stockholders’ equity					0.0
Adjustments for New Accounting Pronouncement
Balance Sheet Classification [Abstract]
Prepaid expenses and other					275.6
Current assets held for sale					3,535.2
Total current assets					7,740.3
Deferred income taxes (noncurrent assets)					179.7
Total assets					17,722.4
Other accrued liabilities					1,180.7
Current liabilities held for sale					734.8
Total current liabilities					3,412.8
Deferred income taxes (liabilities)					991.0
Other noncurrent liabilities					1,369.1
Total liabilities					12,469.2
Retained deficit					(2,511.3)
Stockholders’ equity attributable to parent					5,218.4
Total stockholders’ equity					5,253.2
Total liabilities and stockholders’ equity					17,722.4
Income Statement Classification [Abstract]
Income (loss) from discontinued operations, net of tax					(152.9)
Net income (loss)					$ (6,942.5)
Basic:
Income (loss) from continuing operations (in USD per share)					$ (14.33)
Income (loss) from discontinued operations (in USD per share)					(0.32)
Net income (loss) (in USD per share)					(14.65)
Diluted:
Income (loss) from continuing operations (in USD per share)					(14.33)
Income (loss) from discontinued operations (in USD per share)					(0.32)
Net income (loss) (in USD per share)					$ (14.65)
As Revised
Balance Sheet Classification [Abstract]
Prepaid expenses and other					$ 275.6
Current assets held for sale					3,535.2
Total current assets					7,740.3
Deferred income taxes (noncurrent assets)					179.7
Total assets					17,722.4
Other accrued liabilities					1,181.5
Current liabilities held for sale					750.8
Total current liabilities					3,429.6
Deferred income taxes (liabilities)					975.1
Other noncurrent liabilities					1,368.2
Total liabilities					12,469.2
Retained deficit					(2,511.3)
Stockholders’ equity attributable to parent					5,218.4
Total stockholders’ equity					5,253.2
Total liabilities and stockholders’ equity					$ 17,722.4