Consolidated Statements Of Comprehensive Income (Loss) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Net income (loss) before attribution of noncontrolling interests	$ 468.2	$ (848.0)	$ 1,034.0
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	53.4	4.3	9.7
Net unrealized gains (losses) on available for sale securities	(10.6)	(6.3)	(7.1)
Changes in benefit plans net gain (loss) and prior service (cost)/credit	10.8	4.0	(10.8)
Other comprehensive income (loss), net of tax	53.6	2.0	(8.2)
Comprehensive income (loss) before noncontrolling interests	521.8	(846.0)	1,025.8
Comprehensive loss attributable to noncontrolling interests	0.0	0.0	0.1
Comprehensive income (loss)	$ 521.8	$ (846.0)	$ 1,025.9