Fair Value Measurements - Level 3 Financial Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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]	Mar. 31, 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	7.00%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Fixed Maturities And Equity Securities		$ 17,777	$ 16,627	$ 1,198	$ 1,190	$ 619	$ 603	$ 610	$ 593							$ 443	$ 417	$ 366	$ 305							$ 88	$ 111	$ 48	$ 59
Liquidity adjustment to discount rates used to value fixed maturities and equity securities										5.30%	6.20%	0.40%	0.60%	1.60%	1.70%					4.90%	3.70%	0.80%	0.80%	1.90%	2.00%
Adjustment to discount rates used to value fixed maturities and equity securities for weighting of credit spreads										24.10%	20.90%	1.30%	1.20%	3.00%	2.90%
Percentage of fixed maturities classified in Level 3 that represent single, unadjusted, non-binding broker quotes	10.00%
Percentage of Level 3 securities valued at transaction price	10.00%