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Income Taxes - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020
UNITED KINGDOM
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		$ 4
Foreign Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		6
Deferred Tax Assets, Valuation Allowance		10
Other Assets [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Other		410
Deferred Tax Asset [Domain] \| UNITED STATES
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		3
Deferred Tax Asset [Domain] \| UNITED KINGDOM
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards		2
Scenario, Plan [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Other		$ 205
Forecast [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Other	$ 205