Long Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2012
2.13% to 6.15%, due 2016 to 2042
Debt Instrument [Line Items]
Interest rate, minimum	2.13%
Interest rate, maximum	6.15%
2.13% to 6.15%, due 2016 to 2042 | Minimum
Debt Instrument [Line Items]
Long-term debt maturity year	2016
2.13% to 6.15%, due 2016 to 2042 | Maximum
Debt Instrument [Line Items]
Long-term debt maturity year	2042
7.00% To 7.75%, Due 2013 To 2036
Debt Instrument [Line Items]
Interest rate, minimum	7.00%
Interest rate, maximum	7.75%
7.00% To 7.75%, Due 2013 To 2036 | Minimum
Debt Instrument [Line Items]
Long-term debt maturity year	2013
7.00% To 7.75%, Due 2013 To 2036 | Maximum
Debt Instrument [Line Items]
Long-term debt maturity year	2036