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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount, before tax, of increase (decrease) in the cumulative translation adjustment from gain (loss) on foreign currency derivatives that are designated as, and are effective as, economic hedges of a net investment in a foreign entity.

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Hedging Activities - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
Hedging Activities - Narrative (Details) $ in Millions	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 EUR (€)	Sep. 30, 2018 GBP (£)	Sep. 30, 2018 USD ($)	Mar. 31, 2018 GBP (£)	Mar. 31, 2018 USD ($)	Sep. 30, 2017 EUR (€)
Derivative [Line Items]
Long-term debt outstanding							$ 7,694		$ 7,880
Gains from net investment hedges recorded in other comprehensive income	$ 23	$ 63	$ 184	$ 177
Gains (losses) from cash flow hedges	2	(3)	2	11
Foreign Exchange Contract \| Derivatives not Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments							40		29
Cross Currency Swap \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments							3,279		3,279
Forward Contracts \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments							$ 162		$ 162
Net Investment Hedging \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Derivatives used in net investment hedge, gains (loss) gross	5		39
Net Investment Hedging \| Cross Currency Swap \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments \| £								£ 432,000,000
Term Loan
Derivative [Line Items]
Gains from net investment hedges recorded in other comprehensive income		$ (63)		$ (177)
Derivatives used in net investment hedge, gains (loss) gross	$ 5		$ 39
Euro Denominated Notes \| Term Loan
Derivative [Line Items]
Long-term debt outstanding \| €					€ 1,950,000,000.00					€ 1,200,000,000.00
British Pound Sterling Denominated Notes \| Term Loan
Derivative [Line Items]
Long-term debt outstanding \| £						£ 450,000,000