Bank segment - Repurchase Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Gross amount of recognized liabilities	$ 165	$ 229
Securities Sold under Agreements to Repurchase, Asset	0	0
Securities sold under agreements to repurchase	165	229
Securities sold under agreements to repurchase collateral, financial instruments	204	261
Securities sold under agreements to repurchase, cash collateral pledged	0	0
Financial Institution
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	50	50
Securities sold under agreements to repurchase collateral, financial instruments	53	56
Securities sold under agreements to repurchase, cash collateral pledged	0	0
Government Entities
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	14	56
Securities sold under agreements to repurchase collateral, financial instruments	16	61
Securities sold under agreements to repurchase, cash collateral pledged	0	0
Commercial account holders
Offsetting Liabilities [Line Items]
Securities sold under agreements to repurchase	101	123
Securities sold under agreements to repurchase collateral, financial instruments	135	144
Securities sold under agreements to repurchase, cash collateral pledged	$ 0	$ 0