Segment Information - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Unearned voluntary protection contract revenues		$ 2,400		$ 2,400
Unearned amounts in voluntary protection contract revenues, recognized	$ 182	$ 180	$ 374	$ 368
Other liabilities [Member]
Segment Reporting Information [Line Items]
Unearned voluntary protection contract revenues	$ 2,600		$ 2,600		$ 2,500	$ 2,400
Accounting Standards Update 2014-09 [Member]
Segment Reporting Information [Line Items]
Percentage of voluntary protection contract revenues	82.00%	82.00%	83.00%	83.00%