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Hedging Activities - Narrative (Details) £ in Millions, $ in Millions, $ in Billions	3 Months Ended		9 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 CAD ($)	Dec. 31, 2019 EUR (€)	Dec. 31, 2019 GBP (£)	Sep. 30, 2019 GBP (£)	Mar. 31, 2019 USD ($)	Mar. 31, 2019 CAD ($)	Mar. 31, 2019 EUR (€)	Mar. 31, 2019 GBP (£)	Dec. 31, 2018 EUR (€)	Dec. 31, 2018 GBP (£)
Derivative [Line Items]
Long-term debt outstanding	$ 7,700		$ 7,700						$ 7,600
Gains (losses) on non-derivative net investment hedge	(3)		26
Gains from fair value hedges recorded in earnings	44		44
Gains from cash flow hedges recorded within other comprehensive income	8	$ 35	33	$ 37
Derivatives designated for hedge accounting
Derivative [Line Items]
Gain (loss) from net investment hedges recorded within other comprehensive income	(59)	39	(8)	223
Forward contracts to hedge Euro against British Pound cash flows | Derivatives not Designated for Hedge Accounting
Derivative [Line Items]
Notional values of financial instruments	23		23						28
Forward contracts to offset impact of ineffectiveness of net investment hedges | Derivatives not Designated for Hedge Accounting
Derivative [Line Items]
Gain (loss) on net investment hedges	3		(36)
Notional values of financial instruments | €						€ 250,000,000
Net Investment Hedging | Derivatives designated for hedge accounting
Derivative [Line Items]
Derivatives used in net investment hedge, gains (loss) gross	(20)	63	(11)	102
Net Investment Hedging | November 2018 cross currency swaps | Derivatives designated for hedge accounting
Derivative [Line Items]
Gain (loss) on net investment hedges			34
Notional values of financial instruments					$ 1.5					$ 1.5		£ 932
Proceeds from termination of derivative instruments			84
Cash Flow Hedging | Derivatives designated for hedge accounting
Derivative [Line Items]
Gains from cash flow hedges recorded within other comprehensive income	5	$ 40	40	$ 42
Cash Flow Hedging | Forward contracts | Derivatives designated for hedge accounting
Derivative [Line Items]
Notional values of financial instruments	81		81						81
Cash Flow Hedging | Cross currency swap | Derivatives designated for hedge accounting
Derivative [Line Items]
Notional values of financial instruments	$ 2,900		$ 2,900						$ 2,900
Euro Denominated Notes | Term Loan
Derivative [Line Items]
Long-term debt outstanding | €						250,000,000							€ 1,950,000,000
Euro Denominated Notes | Term Loan | Net Investment Hedging
Derivative [Line Items]
Long-term debt outstanding | €						€ 1,700,000,000					€ 1,950,000,000
British Pound Sterling Denominated Notes | Term Loan
Derivative [Line Items]
Long-term debt outstanding | £							£ 450	£ 450				£ 450		£ 450

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