Income Taxes - Income Tax Contingencies (Details) $ in Millions, ₩ in Billions	3 Months Ended			12 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 KRW (₩)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 KRW (₩)
Income Tax Disclosure [Abstract]
Increase (decrease) in additional liabilities related to unrecognized tax liabilities				$ 9.5	$ (1.8)
Increase (decrease) in assets related to unrecognized tax assets				(4.1)	4.3
Increase (decrease) in unrecognized tax liabilities related to a foreign currency translation expense				(0.2)	0.9
Unrecognized tax liabilities				84.0	70.2
Unrecognized tax assets				25.5	29.7
Reconciliation of total amounts of unrecognized income tax benefits
Gross Unrecognized Tax Liabilities – opening balance				57.0	58.8	$ 62.2
Gross increases – tax positions in prior period				12.2	3.6	10.9
Gross decreases – tax positions in prior period				(13.5)	(10.6)	0.0
Gross increases – tax positions in current period				14.9	11.5	10.7
Gross decreases – tax positions in current period				0.0	0.0	0.0
Settlements				(1.4)	(1.5)	(23.0)
Lapse of statute of limitations				(2.7)	(4.8)	(2.1)
Gross Unrecognized Tax Liabilities – ending balance				66.5	57.0	58.8
Expected reduction in income tax expense if uncertain tax positions are settled by the taxing authorities in the entity's favor				$ 41.1
Expected reduction in effective income tax rate if uncertain tax positions are settled by the taxing authorities in the entity's favor (as a percent)				17.30%
Amount of unrecognized income tax liabilities may decrease within the next twelve months				$ 9.0
Interest related to unrecognized tax benefits, recorded as income (expense)				4.6	1.2	3.4
Penalties related to unrecognized tax benefits, recorded as income tax income (expense)				(0.2)	1.9	0.1
Accrued interest related to unrecognized tax benefits				13.1	8.5
Accrued penalties related to unrecognized tax benefits				$ 4.4	$ 4.6
Assessment | South Korea (SRTO)
Income Tax Contingency [Line Items]
Pre-assessment notice, amount		$ 17.4	₩ 20.1			$ 9.8	₩ 11.3
Foreign Tax Authority | Danish Tax Authority
Income Tax Contingency [Line Items]
Proposed income adjustment	$ 1.7