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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)	3 Months Ended		9 Months Ended
Hedging Activities - Narrative (Details)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 GBP (£)	Nov. 30, 2018 CAD ($)	Nov. 30, 2018 GBP (£)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 GBP (£)	Dec. 31, 2017 EUR (€)
Derivative [Line Items]
Long-term debt outstanding						$ 8,736,000,000				$ 7,880,000,000
Gains (losses) from net investment hedges recorded in other comprehensive income	$ 39,000,000	$ (28,000,000)	$ 223,000,000	$ (205,000,000)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	35,000,000	(16,000,000)	37,000,000	(5,000,000)
Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	40,000,000	$ 0	42,000,000	$ 0
Foreign Exchange Contract \| Derivatives not Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments						10,000,000				29,000,000
Cross Currency Swap \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments						3,279,000,000				3,412,000,000
Forward Contracts \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments						$ 162,000,000				$ 162,000,000
Net Investment Hedging \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Derivatives used in net investment hedge, gains (loss) gross	$ 63,000,000		$ 102,000,000
Net Investment Hedging \| November 2018 Cross Currency Swaps \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments								$ 1,000,000,000	£ 500,000,000
Net Investment Hedging \| March 2018 Cross Currency Swaps \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments \| £											£ 432,000,000
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
Minimum \| Forward Contracts \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Contract maturity dates			Mar. 31, 2019
Maximum \| Forward Contracts \| Derivatives Designated for Hedge Accounting
Derivative [Line Items]
Contract maturity dates			Mar. 31, 2020