Business Developments And Risks And Uncertainties (Narrative) (Detail) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Number of operating segments	3
Cutwater sale effective date	Jan. 01, 2015
Mbia Inc [Member]
Business Acquisition [Line Items]
Gain on sale of subsidiary		$ 24
Liquid assets	$ 497	497	$ 498
Amount released from tax escrow account		228
National [Member]
Business Acquisition [Line Items]
Impairment of real estate		$ 4
Treasury stock shares acquired | shares		8.0
Shares repurchased under share repurchase program, average price per share | $ / shares		$ 8.77
Warburg Pincus [Member]
Business Acquisition [Line Items]
Common Stock Shares Sold | shares		27.3