Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Current period adjustment in other comprehensive income reflecting gains or losses on foreign currency transactions that are designated as, and are effective as, hedges of a net investment in a foreign entity, net of tax effect.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64808268&loc=d3e32211-110900

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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Financial Instruments - (Narratives) (Details)	3 Months Ended
Financial Instruments - (Narratives) (Details)	Mar. 31, 2018 USD ($)	Jul. 31, 2017 GBP (£)	Jul. 31, 2017 EUR (€)	Jul. 10, 2017 GBP (£)	Jul. 10, 2017 EUR (€)	Jun. 30, 2017 GBP (£) instrument	Jun. 30, 2017 EUR (€) instrument
Senior notes, GBP notes due 2022, interest payable at 1.700%
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Face amount of loans \| £		£ 300,000,000
Interest rate swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Notional amount \| $	$ 0
Currency forward contract \| Net investment hedging
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Notional amount						£ 298,000,000	€ 999,000,000
Number of instruments held \| instrument						2	2
Amount of loss reclassified from AOCE into income \| $	$ 38,000,000
Senior notes
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Face amount of loans				£ 300,000,000	€ 1,000,000,000
Senior notes \| Senior notes, Euro notes due 2021, interest payable at 0.400%
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Face amount of loans \| €			€ 500,000,000		500,000,000
Senior notes \| Senior notes, Euro notes due 2024, interest payable at 1.100%
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Face amount of loans \| €			€ 500,000,000		€ 500,000,000
Senior notes \| Senior notes, GBP notes due 2022, interest payable at 1.700%
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Face amount of loans \| £				£ 300,000,000