Bank subsidiary (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Repurchase agreements
Gross amount of recognized liabilities	$ 138	$ 146
Net amount of liabilities presented in the Balance Sheet	138	146
Gross amount not offset in the Balance Sheet
Net amount of liabilities presented in the Balance Sheet	138	146
Financial instruments	138	146
Financial institution
Repurchase agreements
Net amount of liabilities presented in the Balance Sheet	50	50
Gross amount not offset in the Balance Sheet
Net amount of liabilities presented in the Balance Sheet	50	50
Financial instruments	50	50
Commercial account holders
Repurchase agreements
Net amount of liabilities presented in the Balance Sheet	88	96
Gross amount not offset in the Balance Sheet
Net amount of liabilities presented in the Balance Sheet	88	96
Financial instruments	$ 88	$ 96