Significant Accounting Policies (Details) (USD $) In Billions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Significant Accounting Policies
Assets under care	$ 4.2	$ 3.8
Maximum estimated economic life	5 years
Buildings and improvements | Minimum
Premises and Equipment
Estimated Useful Life	3 years
Buildings and improvements | Maximum
Premises and Equipment
Estimated Useful Life	40 years
Furniture and equipment | Minimum
Premises and Equipment
Estimated Useful Life	2 years
Furniture and equipment | Maximum
Premises and Equipment
Estimated Useful Life	10 years