Debt and Credit Arrangements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 24, 2012
Long Term Debt	$ 3,575	$ 3,575
Interest costs incurred	224	245	248
Interest paid	220	244	244
Maximum unsecured borrowings permitted under credit agreement	500
Maximum facility amount permitted to request an increase in the credit available	750
Terminated unsecured borrowings				500
5.2% notes due April 1, 2013 [Member]
Interest rate due on notes and debentures	5.20%
Long Term Debt	275	275
5.75% notes due May 15, 2018 [Member]
Interest rate due on notes and debentures	5.75%
Long Term Debt	600	600
6.6% debentures due August 15, 2018 [Member]
Interest rate due on notes and debentures	6.60%
Long Term Debt	100	100
6.8% debentures due November 15, 2031 [Member]
Interest rate due on notes and debentures	6.80%
Long Term Debt	200	200
6% notes due May 11, 2037 [Member]
Interest rate due on notes and debentures	6.00%
Long Term Debt	800	800
6.5% notes due May 15, 2038 [Member]
Interest rate due on notes and debentures	6.50%
Long Term Debt	600	600
6.375% capital securities due March 29, 2067 [Member]
Long Term Debt	$ 1,000	$ 1,000
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