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Pension Benefits - Narrative (Details) | 1 Months Ended | 3 Months Ended | 12 Months Ended
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Jun. 30, 2019 USD ($) participant | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2021 USD ($) $ / shares | Mar. 31, 2020 USD ($) | Mar. 31, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Actuarial losses from pension plans |  |  |  |  |  | $ 0 | $ 127,000,000 | $ 0
Percentage of eligible compensation (up to percent) |  |  |  |  |  | 75.00% |  |
Contribution expenses |  |  |  |  |  | $ 102,000,000 | 102,000,000 | 92,000,000
First Part Of Pay Contribution |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Company match employee contributions (as a percent) |  |  |  |  |  | 100.00% |  |
Employee contributions (as a percent) |  |  |  |  |  | 3.00% |  |
Second Part Of Pay Contribution |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Company match employee contributions (as a percent) |  |  |  |  |  | 50.00% |  |
Employee contributions (as a percent) |  |  |  |  |  | 2.00% |  |
Held-for-sale | German Wholesale Business |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Pension liabilities derecognized |  | $ 187,000,000 |  |  |  |  |  |
Accumulated other comprehensive loss derecognized |  | 33,000,000 |  |  |  |  |  |
Pension Plans, Defined Benefit |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Unexpected actuarial losses (as a percent) (exceeding) |  |  |  |  |  | 10.00% |  |
Expected benefit payments in 2022 |  |  |  |  |  | $ 43,000,000 |  |
Expected benefit payments in 2023 |  |  |  |  |  | 36,000,000 |  |
Expected benefit payments in 2024 |  |  |  |  |  | 37,000,000 |  |
Expected benefit payments in 2025 |  |  |  |  |  | 36,000,000 |  |
Expected benefit payments in 2026 |  |  |  |  |  | 38,000,000 |  |
Expected benefit payments in 2027 through 2031 |  |  |  |  |  | 202,000,000 |  |
Expected contributions in next fiscal year |  |  |  |  |  | $ 24,000,000 |  |
Unit value of cash and cash equivalents (in dollars per share) | $ / shares |  |  |  |  |  | $ 1.00 |  |
UNITED STATES | Pension Plans, Defined Benefit |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Number of plan participants elected to receive settlement payments | participant | 1,300 |  |  |  |  |  |  |
Settlement payments made | $ 49,000,000 |  |  |  |  |  |  |
Pre-tax pension settlement charges |  |  |  | $ 105,000,000 | $ 17,000,000 |  | 122,000,000 |
Annuity contracts purchased |  |  |  | $ 280,000,000 |  |  |  |
Accumulated other comprehensive loss |  |  |  |  |  | $ 0 |  |
Current liabilities |  |  |  |  |  | 1,000,000 | 1,000,000 |
Actuarial gain (loss) |  |  |  |  |  | $ 0 | $ (20,000,000) |
Weighted-average discount rates for actuarial present value of benefit obligations (percent) |  |  |  |  |  | 2.35% | 3.08% |
Actuarial loss |  |  |  |  |  | $ 0 | $ 129,000,000 | 9,000,000
Projected benefit obligation |  |  |  |  |  | $ 9,000,000 | $ 10,000,000 | 439,000,000
Discount rates (percent) |  |  |  |  |  | 2.35% | 3.08% |
Increase (decrease) in basis points |  |  |  |  |  | 0.0073 |  |
UNITED STATES | Pension Plans, Defined Benefit | German Wholesale Business |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Current liabilities |  |  |  |  |  |  | $ 151,000,000 |
Actuarial loss |  | $ 33,000,000 |  |  |  |  |  |
UNITED STATES | Pension Plans, Defined Benefit | Unfunded plan |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Pre-tax pension settlement charges |  |  | $ 11,000,000 |  |  |  |  |
Amounts of plan exceeding total plan contribution |  |  | $ 114,000,000 |  |  |  |  |
Accumulated pension obligation |  |  |  |  |  |  | 1,000,000 | 12,000,000
Projected benefit obligation |  |  |  |  |  | $ 9,000,000 | 10,000,000 |
Non-U.S. Plans | Pension Plans, Defined Benefit |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Amounts of plan exceeding total plan contribution |  |  |  |  |  | 22,000,000 | 17,000,000 | $ 27,000,000
Current liabilities |  |  |  |  |  | 9,000,000 | 162,000,000 |
Actuarial gain (loss) |  |  |  |  |  | (89,000,000) | 36,000,000 |
Actuarial loss resulting from discount rate changes |  |  |  |  |  | $ 32,000,000 | $ 6,000,000 |
Weighted-average discount rates for actuarial present value of benefit obligations (percent) |  |  |  |  |  | 1.89% | 2.03% | 2.13%
Actuarial gain (loss) resulting from demographic and assumption changes |  |  |  |  |  | $ (57,000,000) | $ 42,000,000 |
Actuarial gain (loss) resulting from the difference between actual inflation and assumed inflation |  |  |  |  |  |  | 23,000,000 |
Actuarial loss |  |  |  |  |  | 35,000,000 | 6,000,000 | $ 5,000,000
Projected benefit obligation |  |  |  |  |  | $ 875,000,000 | $ 896,000,000 | $ 990,000,000
Discount rates (percent) |  |  |  |  |  | 1.89% | 2.03% | 2.13%
Increase (decrease) in basis points |  |  |  |  |  | 0.0014 |  |
Percentage of total plan contribution - exceeding (percent) |  |  |  |  |  | 5.00% |  |
Funded status (as a percent) |  |  |  |  |  | 78.00% |  |
Amounts accrued for liability |  |  |  |  |  | $ 0 |  |
Non-U.S. Plans | Pension Plans, Defined Benefit | Norwegian Public Service Pension Fund (SPK) |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Amount of plan asset value |  |  |  |  |  | 36,000,000 | $ 29,000,000 |
Non-U.S. Plans | Pension Plans, Defined Benefit | Unfunded plan |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Projected benefit obligation |  |  |  |  |  | $ 162,000,000 | 298,000,000 |
Termination of U.S Defined Benefit Pension Plan and Settlement of Retirement Benefits | UNITED STATES | Pension Plans, Defined Benefit |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Actuarial loss |  |  |  |  |  |  | 127,000,000 |
Termination of U.S Defined Benefit Pension Plan | UNITED STATES | Pension Plans, Defined Benefit |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Actuarial losses from pension plans |  |  |  |  |  |  | 116,000,000 |
Settlement of Executive Retirement Benefits | Retired executive | UNITED STATES | Pension Plans, Defined Benefit |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |
Actuarial losses from pension plans |  |  |  |  |  |  | $ 11,000,000 |

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