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Hedging Activities - Narrative (Details) € in Millions, £ in Millions, $ in Millions | 3 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |  |  |  |
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Mar. 31, 2025 CAD ($) | Jun. 30, 2023 USD ($) | Mar. 31, 2025 USD ($) | Mar. 31, 2024 USD ($) | Mar. 31, 2023 USD ($) | Apr. 30, 2025 USD ($) | Mar. 31, 2025 EUR (€) | Mar. 31, 2025 GBP (£) | Mar. 31, 2025 CAD ($) | Dec. 31, 2024 GBP (£) | Dec. 31, 2024 CAD ($) | Jun. 30, 2024 CAD ($) | Mar. 31, 2024 EUR (€) | Mar. 31, 2024 GBP (£) | Mar. 31, 2024 CAD ($) | Jun. 15, 2023 USD ($) | Mar. 31, 2023 EUR (€) | Feb. 28, 2023 GBP (£) | Dec. 31, 2022 GBP (£) | Sep. 30, 2022 EUR (€) | Mar. 31, 2022 EUR (€)
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  | $ 5,654,000,000 | $ 5,629,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss), cash flow hedge, gain (loss), reclassification before tax |  |  | 0 | 0 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on derivative termination |  |  |  |  | 97,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value Hedges | Derivatives designated for hedge accounting: | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  | 1,300,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, notional mount, terminated |  |  | 500,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash Flow Hedging | Derivatives designated for hedge accounting: | Currency Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss), cash flow hedge, gain (loss), reclassification before tax |  |  | (4,000,000) | 39,000,000 | (54,000,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash Flow Hedging | Derivatives designated for hedge accounting: | Interest rate swap locks, Foreign currency forwards and Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other comprehensive income (loss), cash flow hedge, gain (loss), reclassification before tax |  |  | (6,000,000) | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash Flow Hedging | Derivatives designated for hedge accounting: | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  | $ 850,000,000 |  |  |  |  |  |  |  |  |  |  |  |  | $ 500,000,000 |  |  |  |  |
Derivative, notional mount, terminated |  |  |  |  | 500,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, notional amount, entered into during period |  | $ 50,000,000 |  |  | 450,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, termination proceeds, amortization period |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain on derivative termination |  |  |  |  | 97,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash Flow Hedging | Derivatives designated for hedge accounting: | Interest Rate Swap | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  |  |  |  | $ 550,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
British Pound Sterling Denominated Notes | Loans payable |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt | £ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | £ 450 |  |
EUR | Fair Value Hedges | Derivatives designated for hedge accounting: | Currency Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative | € |  |  |  |  |  |  | € 1,100 |  |  |  |  |  | € 1,100 |  |  |  |  |  |  |  |
EUR | Currency Swap | Net Investment Hedging | Derivatives designated for hedge accounting: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative | € |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | € 1,100 |  |  | € 1,100 | € 1,100
EUR | Currency Swap | Fair Value Hedges | Derivatives designated for hedge accounting: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | € 1,100 | £ 450 |  |  |
USD | Fair Value Hedges | Derivatives designated for hedge accounting: | Interest Rate Swap Entered Into YTD |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  |  |  | 1,300,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
USD | Fair Value Hedges | Derivatives designated for hedge accounting: | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  | $ 750,000,000 | 1,250,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
USD | Cash Flow Hedging | Derivatives designated for hedge accounting: | Interest Rate Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  | $ 850,000,000 | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
GBP | Fair Value Hedges | Derivatives designated for hedge accounting: | Currency Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative | £ |  |  |  |  |  |  |  | £ 450 |  |  |  |  |  | £ 450 |  |  |  |  |  |  |
GBP | Cash Flow Hedging | Derivatives designated for hedge accounting: | Interest rate swap locks, Foreign currency forwards and Other |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative | £ |  |  |  |  |  |  |  | £ 11 |  | £ 45 |  |  |  | £ 39 |  |  |  |  |  |  |
CAD | Net Investment Hedging | Derivatives designated for hedge accounting: | Currency Swap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amounts of derivative |  |  |  |  |  |  |  |  | $ 6,500 |  | $ 6,000 | $ 2,500 |  |  | $ 1,500 |  |  |  |  |  |
Derivative, notional mount, terminated |  |  |  |  |  |  |  |  |  |  | $ 5,000 | $ 1,500 |  |  |  |  |  |  |  |  |
Derivative, notional amount, entered into during period | $ 3,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disposed of by Sale | European Businesses (Disposal Group) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification from AOCI, current period, before tax |  |  |  |  | 112,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disposed of by Sale | U.K. Businesses (Disposal Group) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reclassification from AOCI, current period, before tax, attributable to parent |  |  |  |  | $ 26,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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