Fair Value Measurements Changes in Fair Value Level 3 (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Investment Segment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ (12)	$ (33)
Other Segments and Holding Company [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Net realized and unrealized losses	(28)	(97)
Fair Value, Measurements, Recurring [Member] | Investment Segment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	63	75	$ 75	$ 287
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Net realized and unrealized losses	(12)	(100)
Distribution-in-kind	0	(110)
Gross proceeds	0	(2)
Fair Value, Measurements, Recurring [Member] | Other Segments and Holding Company [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	182	153	$ 154	$ 138
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Transfer out	(46)	0
Net realized and unrealized losses	(28)	(97)
Purchases, additions and settlements, net	102	2
Distribution-in-kind	0	110
Fair Value, Measurements, Recurring [Member] | Holding Company [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Distribution-in-kind		$ 110
Available-for-sale Securities [Member] | Fair Value, Measurements, Recurring [Member] | Holding Company [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	100
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, [Roll Forward]
Purchases, additions and settlements, net	$ 100