Debt and Credit Arrangements - Long Term Debt (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Long Term Debt	$ 3,575	$ 3,575
5.2% notes due April 1, 2013 [Member]
Debt Instrument [Line Items]
Long Term Debt	275	275
5.75% notes due May 15, 2018 [Member]
Debt Instrument [Line Items]
Long Term Debt	600	600
6.6% debentures due August 15, 2018 [Member]
Debt Instrument [Line Items]
Long Term Debt	100	100
6.8% debentures due November 15, 2031 [Member]
Debt Instrument [Line Items]
Long Term Debt	200	200
6% notes due May 11, 2037 [Member]
Debt Instrument [Line Items]
Long Term Debt	800	800
6.5% notes due May 15, 2038 [Member]
Debt Instrument [Line Items]
Long Term Debt	600	600
6.375% capital securities due March 29, 2067 [Member]
Debt Instrument [Line Items]
Long Term Debt	$ 1,000	$ 1,000