Debt and Credit Arrangements (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Debt and Credit Arrangements (Textual) [Abstract]
Long Term Debt	$ 3,575	$ 3,975
Additional Debt and Credit Arrangements (Textual) [Abstract]
Interest costs incurred	245	248	248
Interest paid	244	244	244
Maximum unsecured borrowings permitted under credit agreement	500
6% notes due November 15, 2011 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate due on notes and debentures	6.00%
Long Term Debt	0	400
5.2% notes due April 1, 2013 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate due on notes and debentures	5.20%
Long Term Debt	275	275
5.75% notes due May 15, 2018 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate due on notes and debentures	5.75%
Long Term Debt	600	600
6% notes due May 11, 2037 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate due on notes and debentures	6.00%
Long Term Debt	800	800
6.5% notes due May 15, 2038 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate due on notes and debentures	6.50%
Long Term Debt	600	600
6.6% debentures due August 15, 2018 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate due on notes and debentures	6.60%
Long Term Debt	100	100
6.8% debentures due November 15, 2031 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate due on notes and debentures	6.80%
Long Term Debt	200	200
6.375% capital securities due March 29, 2067 [Member]
Debt and Credit Arrangements (Textual) [Abstract]
Interest rate of capital securities through April 14, 2017	6.375%
Interest rate on capital securities after April 14, 2017, plus three-month LIBOR rate	2.25%
Consecutive years payment of interest may be deferred on capital securities	10 years
Long Term Debt	$ 1,000	$ 1,000