Bank segment - Repurchase Agreements (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Offsetting Liabilities [Line Items]
Gross amount of recognized liabilities	$ 111,000,000	$ 65,000,000
Gross amount offset in the Balance Sheets	0	0
Securities sold under agreements to repurchase	111,000,000	65,000,000
Commercial account holders
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	111,000,000	65,000,000
Securities sold under agreements to repurchase collateral, financial instruments	128,000,000	92,000,000
Securities sold under agreements to repurchase, cash collateral pledged	0	0
American Savings Bank (ASB)
Offsetting Liabilities [Line Items]
FHLB advances	0
Securities sold under agreements to repurchase	$ 111,000,000	$ 65,000,000