Pension Benefits - Narrative (Details)	1 Months Ended	3 Months Ended				12 Months Ended
	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