v3.26.1
U.S. and Europe Retrospective Responsibility Plans - Schedule of Preferred Stock As-Converted Value and Book Value (Details)
$ / shares in Units, shares in Millions, $ in Millions
Mar. 31, 2026
USD ($)
$ / shares
shares
Sep. 30, 2025
USD ($)
$ / shares
shares
Restricted Cash and Cash Equivalent Item [Line Items]    
As-converted Value of Preferred Stock $ 1,131 $ 1,389
Book value of preferred stock 528 745
Book Value of Preferred Stock, Total 123 232
Less: right to recover for covered losses (44) (124)
As-converted Value of Preferred Stock, Total recovery for covered losses available 1,087 1,265
Book Value of Preferred of Stock, Total recovery for covered losses available $ 79 $ 108
Preferred stock, shares outstanding (in shares) | shares 5 5
Share price (in dollars per share) | $ / shares $ 302.24 $ 341.38
Series B preferred stock    
Restricted Cash and Cash Equivalent Item [Line Items]    
As-converted Value of Preferred Stock $ 447 $ 566
Book value of preferred stock $ 7 $ 67
Preferred stock, shares outstanding (in shares) | shares 2 2
Preferred stock, conversion rate (in percent) 0.5960 0.6690
Series C preferred stock    
Restricted Cash and Cash Equivalent Item [Line Items]    
As-converted Value of Preferred Stock $ 684 $ 823
Book value of preferred stock $ 116 $ 165
Preferred stock, shares outstanding (in shares) | shares 3 3
Preferred stock, conversion rate (in percent) 0.7170 0.7640