Debt and Credit Arrangements - Long Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2013
Debt Instrument [Line Items]
Interest rate of capital securities march 29, 2067	6.375%
5.2% notes due April 1, 2013 [Member]
Debt Instrument [Line Items]
Interest rate due on notes and debentures	5.20%
5.75% notes due May 15, 2018 [Member]
Debt Instrument [Line Items]
Interest rate due on notes and debentures	5.75%
6.6% debentures due August 15, 2018 [Member]
Debt Instrument [Line Items]
Interest rate due on notes and debentures	6.60%
6.8% debentures due November 15, 2031 [Member]
Debt Instrument [Line Items]
Interest rate due on notes and debentures	6.80%
6% notes due May 11, 2037 [Member]
Debt Instrument [Line Items]
Interest rate due on notes and debentures	6.00%
6.5% notes due May 15, 2038 [Member]
Debt Instrument [Line Items]
Interest rate due on notes and debentures	6.50%
6.375% capital securities due March 29, 2067 [Member]
Debt Instrument [Line Items]
Interest rate of capital securities march 29, 2067	6.375%