Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 345.0	$ 566.9	$ 306.2
Available-for-sale debt securities:
Change in net unrealized gains and losses, net of tax (provision) benefit of ($1.0), $1.0, and ($4.0) for 2019, 2018, and 2017, respectively	4.6	0.6	4.5
Net realized (gains) losses reclassified into net income, net of tax provisions of $0.1, zero, and $0.9 for 2019, 2018, and 2017, respectively	(0.4)	0.9	(2.1)
Net change on available-for-sale debt securities, net of tax	4.2	1.5	2.4
Cash flow hedges:
Change in net unrealized gains and losses, net of tax (provision) benefit of ($2.6), $2.3, and ($4.4) for 2019, 2018, and 2017, respectively	(8.9)
Change in net unrealized gains and losses, net of tax (provision) benefit of ($2.6), $2.3, and ($4.4) for 2019, 2018, and 2017, respectively		(6.4)	15.7
Net realized losses (gains) reclassified into net income, net of tax provisions of $1.7, $0.3, and $2.4 for 2019, 2018, and 2017, respectively	5.5
Net realized losses (gains) reclassified into net income, net of tax provisions of $1.7, $0.3, and $2.4 for 2019, 2018, and 2017, respectively		(1.2)	(5.2)
Net change on cash flow hedges, net of tax	(3.4)
Net change on cash flow hedges, net of tax		(7.6)	10.5
Change in foreign currency translation adjustments	(1.1)	(12.4)	19.0
Other comprehensive (loss) income, net of tax	(0.3)	(18.5)	31.9
Comprehensive income	$ 344.7	$ 548.4	$ 338.1