Principles of Consolidation and Other Matters - Investment Income (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) investment	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Deferred Revenue Arrangement [Line Items]
Equity method investments lag period			3 months
Investment income (loss) | $	$ 34	$ 26	$ 39	$ 37
Trident III [Member] | Private Equity Funds [Member]
Deferred Revenue Arrangement [Line Items]
Number of investments harvested by investment manager	2