Bank segment - Repurchase Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Offsetting Liabilities [Line Items]
Gross amount of recognized liabilities	$ 269	$ 191
Securities sold under agreements to repurchase	269	191
Securities sold under agreements to repurchase collateral, financial instruments	269	191
Financial Institution
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	50	50
Securities sold under agreements to repurchase collateral, financial instruments	50	50
Government Entities
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	66	56
Securities sold under agreements to repurchase collateral, financial instruments	66	56
Commercial account holders
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	153	85
Securities sold under agreements to repurchase collateral, financial instruments	$ 153	$ 85