Investments and Derivative Instruments (Details Textual 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Variable Interest Entity [Line Items]
Assets	$ 226	$ 258
Other liabilities, variable interest entity liabilities	56	89
Company's maximum exposure to the loss of the contingent capital facility	174	174
Non-Consolidated VIEs [Member]
Variable Interest Entity [Line Items]
Assets	22	23
Other liabilities, variable interest entity liabilities	21	23
Company's maximum exposure to the loss of the contingent capital facility	$ 3	$ 3