Fair Value Measurements - Level 3 Financial Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Valued Using Pricing Models [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Valued Using Pricing Models [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Maximum [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Maximum [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Minimum [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Minimum [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Weighted Average [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Other asset and mortgage-backed securities [Member] Weighted Average [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Valued Using Pricing Models [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Valued Using Pricing Models [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Maximum [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Maximum [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Minimum [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Minimum [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Weighted Average [Member] Unobservable Inputs Developed By Company [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate and government debt securities [Member] Weighted Average [Member] Unobservable Inputs Developed By Company [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate [Member] Valued At Transaction Price [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Corporate [Member] Valued At Transaction Price [Member]	Sep. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Equity securities [Member] Valued At Transaction Price [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value Inputs Level 3 [Member] Equity securities [Member] Valued At Transaction Price [Member]
Fair Value Disclosures [Abstract]
Percentage of investments in fixed maturities and equity securities classified in Level 3	5.00%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fixed Maturities And Equity Securities		$ 18,987	$ 16,627	$ 984	$ 1,190	$ 508	$ 603	$ 501	$ 593							$ 369	$ 417	$ 316	$ 305							$ 64	$ 111	$ 43	$ 59
Liquidity adjustment to discount rates used to value fixed maturities and equity securities										3.50%	6.20%	0.40%	0.60%	1.40%	1.70%					3.40%	3.70%	0.80%	0.80%	1.70%	2.00%
Adjustment to discount rates used to value fixed maturities and equity securities for weighting of credit spreads										25.40%	20.90%	1.40%	1.20%	2.50%	2.90%
Percentage of fixed maturities classified in Level 3 that represent single, unadjusted, non-binding broker quotes	6.00%
Percentage of Level 3 securities valued at transaction price	11.00%