Debt (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Debt Instrument [Line Items]
Repurchased of 10% Debentures	$ 200,000,000	$ 1,018,000,000
Line of Credit Facility, Amount Outstanding			238,000,000
Senior Note 4.75% Due in 2014 [Member]
Debt Instrument [Line Items]
Senior Notes			200,000,000
Interest rate on Note	0.00%
5.125% senior notes due 2022 [Member]
Debt Instrument [Line Items]
Senior Notes	796,000,000		796,000,000
Interest rate on Note	5.125%
6.625% senior notes due 2042 [Member]
Debt Instrument [Line Items]
Senior Notes	178,000,000		178,000,000
Interest rate on Note	6.625%
Senior Note 4.3% Due in 2042 [Member]
Debt Instrument [Line Items]
Senior Notes	298,000,000		298,000,000
Interest rate on Note	4.30%
6.1% senior notes due 2041 [Member]
Debt Instrument [Line Items]
Senior Notes	326,000,000		326,000,000
Interest rate on Note	6.10%
Senior Note 4.0% Due in 2015 [Member]
Debt Instrument [Line Items]
Senior Notes	289,000,000		289,000,000
Interest rate on Note	4.00%
Senior Note 7.3% Due in 2015 [Member]
Debt Instrument [Line Items]
Senior Notes	167,000,000		167,000,000
Interest rate on Note	7.30%
Senior Note 7.5% Due in 2016 [Member]
Debt Instrument [Line Items]
Senior Notes	275,000,000		275,000,000
Interest rate on Note	5.50%
Senior Note 5.375% Due in 2017 [Member]
Debt Instrument [Line Items]
Senior Notes	415,000,000		415,000,000
Interest rate on Note	5.375%
Senior Note 4.0% Due in 2017 [Member]
Debt Instrument [Line Items]
Senior Notes	295,000,000		295,000,000
Interest rate on Note	4.00%
Senior Note 6.3% Due in Two Thousand Eighteen [Member]
Debt Instrument [Line Items]
Senior Notes	320,000,000		320,000,000
Interest rate on Note	6.30%
Senior Note 6.0% Due in 2019 [Member]
Debt Instrument [Line Items]
Senior Notes	413,000,000		413,000,000
Interest rate on Note	6.00%
Senior Note 5.5% Due in 2020 [Member]
Debt Instrument [Line Items]
Senior Notes	499,000,000		499,000,000
Interest rate on Note	5.50%
Senior Note 7.65% Due in 2027 [Member]
Debt Instrument [Line Items]
Senior Notes	80,000,000		79,000,000
Interest rate on Note	7.65%
Senior Note 7.375% Due in 2031 [Member]
Debt Instrument [Line Items]
Senior Notes	63,000,000		63,000,000
Interest rate on Note	7.375%
Senior Note 5.95% Due in 2036 [Member]
Debt Instrument [Line Items]
Senior Notes	299,000,000		298,000,000
Interest rate on Note	5.95%
Senior Note 6.625% Due in 2042 [Member]
Debt Instrument [Line Items]
Senior Notes	295,000,000		295,000,000
Interest rate on Note	6.625%
Junior Subordinated Notes 7.75% Due 2042 [Member]
Debt Instrument [Line Items]
Interest rate on Note	7.875%
Junior Subordinate Notes 8.125% Note Due 2068 [Member]
Debt Instrument [Line Items]
Interest rate on Note	8.125%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum amount available under the line of credit facility	1,750,000,000
Line of credit facility maximum borrowing capacity available to support letters of credit	250,000,000
Ratio of Indebtedness to Net Capital	0.35
Consolidated total debt of subsidiaries to consolidated total capitalization ratio	10.00%
Net worth after tax	14,900,000,000
Senior Note 4.75% Due in 2014 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 0