Capital Structure (Details) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended
	Apr. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Jun. 30, 2014	Jun. 12, 2013
Debt outstanding:
Total long-term debt		$ 5,194,000,000	$ 6,201,000,000
Total debt		5,194,000,000	6,201,000,000
Redemption price as percentage of principal amount plus accrued and unpaid interest		100.00%
Repurchased principal amounts of debt		10,000,000	1,900,000,000
Loss on extinguishment of debt		1,000,000	491,000,000
Period of issuance of common stock prior to dividend declaration date during which dividend declaration is prohibited		90 days
Property and equipment, net		1,031,000,000	1,024,000,000
Unsecured revolving credit facility		1,000,000,000
Commercial Paper maximum borrowing capacity		1,000,000,000
Credit facility extended term	1 year
Additional borrowing capacity under credit facility increase provision		500,000,000
Maximum debt to capital ratio allowed under credit facility covenant (as a percent)		37.50%
Amount outstanding under credit facility		0	0
Interest paid on debt		332,000,000	361,000,000	366,000,000
Common stock
Common stock, shares issued		900,000,000	900,000,000
Common stock, shares outstanding		418,000,000	449,000,000
Treasury stock, shares		482,000,000	451,000,000
Reacquired shares		39,000,000
Average cost of reacquired shares (in dollars per share)		$ 59.21
Reissued net shares under equity incentive plans		8,000,000
Preferred stock
Preferred stock, issued shares		72,200	32,300
Preferred stock, par value (in dollars per share)		$ 1	$ 1
Aggregate liquidation preference		1,805,000,000
Minimum
Preferred stock
Collective risk-based capital ratios of subsidiaries as a percentage of net written premiums of insurance business		80.00%
Percentage of decline in consolidated shareholders' equity from benchmark quarter		20.00%
Maximum
Preferred stock
Risk-based capital ratios as a percentage of action level risk-based capital		175.00%
Percentage by which consolidated shareholders' equity should increase or decrease to avoid restriction on dividends		20.00%
Commercial Paper
Debt outstanding:
Amount of commercial paper outstanding		0	0
Noncumulative Perpetual Preferred Stock
Debt outstanding:
Period after occurrence of certain tax and rating agency events in which redemption of debt in whole permissible		90 days
Preferred stock
Preferred stock, par value (in dollars per share)		$ 1.00
Preferred stock, shares liquidation preference (in dollars per share)		$ 25,000
Preferred stock, redemption price (in dollars per share)		$ 25,000					$ 25,000
Noncumulative Perpetual Preferred Stock | Maximum
Preferred stock
Additional members of the board of directors		2
Noncumulative Perpetual Preferred Stock, Series A
Preferred stock
Preferred stock, issued shares		11,500
Preferred stock stated dividend rate (as a percent)		5.625%
Aggregate liquidation preference		287,500,000
Noncumulative Perpetual Preferred Stock, Series C
Preferred stock
Preferred stock, issued shares		15,400
Preferred stock stated dividend rate (as a percent)		6.75%
Aggregate liquidation preference		385,000,000
Noncumulative Perpetual Preferred Stock, Series D
Preferred stock
Preferred stock, issued shares		5,400
Preferred stock stated dividend rate (as a percent)		6.625%
Aggregate liquidation preference		135,000,000
Noncumulative Perpetual Preferred Stock, Series E
Preferred stock
Preferred stock, issued shares		29,900			29,900
Preferred stock stated dividend rate (as a percent)		6.625%
Aggregate liquidation preference		747,500,000			747,500,000
Noncumulative Perpetual Preferred Stock, Series F
Preferred stock
Preferred stock, issued shares		10,000				10,000
Preferred stock stated dividend rate (as a percent)		6.25%
Aggregate liquidation preference		250,000,000				250,000,000
5.00% Senior Notes, due 2014
Debt outstanding:
Note stated interest rate (as a percent)		5.00%	5.00%
Total long-term debt			650,000,000
6.20% Senior Notes, due 2014
Debt outstanding:
Note stated interest rate (as a percent)		6.20%	6.20%
Total long-term debt			300,000,000
6.75% Senior Debentures, due 2018
Debt outstanding:
Note stated interest rate (as a percent)		6.75%	6.75%
Total long-term debt		176,000,000	177,000,000
Threshold percentage of repurchase or redemption of outstanding principal debentures for non applicability of promises and covenants contained in the new RCC		10.00%
Period within which threshold percentage of outstanding principal of debentures is to be purchased for non applicability of promises and covenants contained in the new RCC		1 year
Specified period within which percentage of outstanding principal of debentures is to be purchased for non applicability of promises and covenants contained in the new RCC		10 years
6.75% Senior Debentures, due 2018 | Maximum
Debt outstanding:
Percentage of repurchase or redemption of outstanding principal debentures within specified period for non applicability of promises and covenants contained in the new RCC		25.00%
7.45% Senior Notes, due 2019
Debt outstanding:
Note stated interest rate (as a percent)		7.45%	7.45%
Total long-term debt		317,000,000	317,000,000
3.15% Senior Notes, due 2023
Debt outstanding:
Note stated interest rate (as a percent)		3.15%	3.15%
Total long-term debt		500,000,000	500,000,000
6.125% Senior Notes, due 2032
Debt outstanding:
Note stated interest rate (as a percent)		6.125%	6.125%
Total long-term debt		159,000,000	159,000,000
5.35% Senior Notes due 2033
Debt outstanding:
Note stated interest rate (as a percent)		5.35%	5.35%
Total long-term debt		323,000,000	323,000,000
5.55% Senior Notes due 2035
Debt outstanding:
Note stated interest rate (as a percent)		5.55%	5.55%
Total long-term debt		546,000,000	546,000,000
5.95% Senior Notes, due 2036
Debt outstanding:
Note stated interest rate (as a percent)		5.95%	5.95%
Total long-term debt		386,000,000	386,000,000
6.90% Senior Debentures, due 2038
Debt outstanding:
Note stated interest rate (as a percent)		6.90%	6.90%
Total long-term debt		165,000,000	165,000,000
5.20% Senior Notes due 2042
Debt outstanding:
Note stated interest rate (as a percent)		5.20%	5.20%
Total long-term debt		62,000,000	72,000,000
4.50% Senior Notes, due 2043
Debt outstanding:
Note stated interest rate (as a percent)		4.50%	4.50%
Total long-term debt		500,000,000	500,000,000
Subordinated Debentures
Debt outstanding:
Minimum principal outstanding amount for redemption of debt in whole or in part		25,000,000
Period after occurrence of certain tax and rating agency events in which redemption of debt in whole permissible		90 days
Interest on debentures payment terms		three-month LIBOR
Maximum period for deferment of interest payment		5 years
5.10% Subordinated Debentures, due 2053
Debt outstanding:
Note stated interest rate (as a percent)		5.10%	5.10%
Total long-term debt		500,000,000	500,000,000
Interest on debentures payment terms		three-month LIBOR
Interest rate spread over LIBOR (as a percent)		3.165%
5.75% Subordinated Debentures, due 2053
Debt outstanding:
Note stated interest rate (as a percent)		5.75%	5.75%
Total long-term debt		800,000,000	800,000,000
Interest on debentures payment terms		three-month LIBOR
Interest rate spread over LIBOR (as a percent)		2.938%
6.125% Junior Subordinated Debentures, due 2067
Debt outstanding:
Note stated interest rate (as a percent)		6.125%	6.125%
Total long-term debt		252,000,000	252,000,000
Interest on debentures payment terms		three-month LIBOR
Interest rate spread over LIBOR (as a percent)		1.935%
6.50% Junior Subordinated Debentures, due 2067
Debt outstanding:
Note stated interest rate (as a percent)		6.50%	6.50%
Total long-term debt		500,000,000	500,000,000
Interest on debentures payment terms		three-month LIBOR
Interest rate spread over LIBOR (as a percent)		2.12%
Synthetic lease VIE obligations, floating rates, due 2014
Debt outstanding:
Total long-term debt			44,000,000
Property and equipment, net			29,000,000
Federal Home Loan Bank ("FHLB") advances, due 2018
Debt outstanding:
Total long-term debt		$ 8,000,000	$ 10,000,000
The Debentures
Debt outstanding:
Maximum period for deferment of interest payment		10 years
Reserved common stock authorized and unissued for debentures obligations (in shares)		75,000,000