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Segment Information - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Apr. 01, 2019
Apr. 01, 2018
Segment Reporting Information [Line Items]            
Unearned insurance premiums and contract revenues   $ 2,200   $ 2,200    
Insurance earned premiums and contract revenues $ 121 $ 178 $ 303 $ 345    
Other liabilities [Member]            
Segment Reporting Information [Line Items]            
Unearned insurance premiums and contract revenues $ 2,300   $ 2,300   $ 2,200 $ 2,200
Accounting Standards Update 2014-09 [Member]            
Segment Reporting Information [Line Items]            
Percentage of insurance earned premiums and contract revenues accounted under guidance for revenue from contracts with customers 84.00% 84.00% 84.00% 84.00%