Bank segment - Other borrowings (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Offsetting Liabilities [Line Items]
Gross amount  of recognized  liabilities	$ 131.0	$ 281.0
Gross amount  offset in the  Balance Sheets	0.0	0.0
Net amount of liabilities presented in the Balance Sheets	131.0	281.0
American Savings Bank (ASB)
Offsetting Liabilities [Line Items]
Advances from the FHLB	0.0	414.0
Commercial account holders
Offsetting Liabilities [Line Items]
Net amount of liabilities presented in the Balance Sheets	131.0	281.0
Financial instruments	172.0	327.0
Cash collateral pledged	$ 0.0	$ 0.0