- Summary of Notes Payable (Parenthetical) (Detail) (JPY ¥) In Billions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
8.50% senior notes due May 2019
Debt Instrument [Line Items]
Notes payable, interest rate	8.50%	8.50%
6.45% senior notes due August 2040
Debt Instrument [Line Items]
Notes payable, interest rate	6.45%	6.45%
6.90% senior notes due December 2039
Debt Instrument [Line Items]
Notes payable, interest rate	6.90%	6.90%
3.45% senior notes due August 2015
Debt Instrument [Line Items]
Notes payable, interest rate	3.45%	3.45%
2.65% senior notes due February 2017
Debt Instrument [Line Items]
Notes payable, interest rate	2.65%	2.65%
4.00% senior notes due February 2022
Debt Instrument [Line Items]
Notes payable, interest rate	4.00%	4.00%
5.50% subordinated notes due September 2052
Debt Instrument [Line Items]
Notes payable, interest rate	5.50%	5.50%
2.26% yen-denominated Uridashi notes due September 2016
Debt Instrument [Line Items]
Notes payable, interest rate	2.26%	2.26%
Notes payable, principal amount	8.0	8.0
1.47% yen-denominated Samurai notes due July 2014
Debt Instrument [Line Items]
Notes payable, interest rate	1.47%	1.47%
Notes payable, principal amount	28.7	28.7
1.84% yen-denominated Samurai notes due July 2016
Debt Instrument [Line Items]
Notes payable, interest rate	1.84%	1.84%
Notes payable, principal amount	15.8	15.8
Variable interest rate yen-denominated Samurai notes due July 2014
Debt Instrument [Line Items]
Notes payable, interest rate	1.32%	1.34%
Notes payable, principal amount	5.5	5.5
3.60% yen-denominated loan due July 2015
Debt Instrument [Line Items]
Notes payable, interest rate	3.60%	3.60%
Notes payable, principal amount	10.0	10.0
3.00% yen-denominated loan due August 2015
Debt Instrument [Line Items]
Notes payable, interest rate	3.00%	3.00%
Notes payable, principal amount	5.0	5.0