Amount after tax, before reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Name:	us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

OTHER COMPREHENSIVE INCOME/(LOSS) - Narrative (Details) £ in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 GBP (£)	Sep. 30, 2021 USD ($)	Dec. 31, 2020 GBP (£)	Dec. 31, 2020 USD ($)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Foreign currency transaction and translation gain (loss)	$ 3.6	$ (5.8)	$ (4.3)	$ 3.6
Designated as Hedging Instrument
Accumulated Other Comprehensive Income (Loss) [Line Items]
Intercompany debt					£ 130	$ 178.8	£ 130	$ 174.5