Bank segment - Repurchase Agreements (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Offsetting Liabilities [Line Items]
Gross amount of recognized liabilities	$ 65	$ 65
Gross amount offset in the Balance Sheets	0	0
Securities sold under agreements to repurchase	65	65
Commercial account holders
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	65	65
Securities sold under agreements to repurchase collateral, financial instruments	90	92
Securities sold under agreements to repurchase, cash collateral pledged	0	0
American Savings Bank (ASB)
Offsetting Liabilities [Line Items]
FHLB advances	25
Securities sold under agreements to repurchase	$ 65	$ 65