Long-Term Debt - Components of Long-Term Debt (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Debt instrument interest rate	1.65%
Real Estate Loans and securities pledged	$ 1,600	$ 428
Senior medium-term notes due through 2021 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2021
Long-term debt weighted average interest rate	5.11%	4.49%
1.100% Subordinated notes due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2028
Debt instrument interest rate	1.10%
6.875% Subordinated notes due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2029
Debt instrument interest rate	6.875%
7.750% Subordinated notes due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2029
Debt instrument interest rate	7.75%
5.700% Subordinated notes due 2035 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2035
Debt instrument interest rate	5.70%
8.000% Subordinated notes due 2068 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2068
Debt instrument interest rate	8.00%
Senior medium-term notes due through 2039 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2039
Senior Euro medium-term notes due through 2013 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2013
Long-term debt weighted average interest rate	0.64%	0.59%
7.413% Subordinated remarketable notes due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2027
Debt instrument interest rate	7.413%
5.70% Subordinated notes due 2012 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2012
Debt instrument interest rate	5.70%
5.80% Subordinated notes due 2014 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2014
Debt instrument interest rate	5.80%
4.95% Subordinated notes due 2015 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2015
Debt instrument interest rate	4.95%
5.45% Subordinated notes due 2016 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2016
Debt instrument interest rate	5.45%
5.70% Subordinated notes due 2017 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2017
Debt instrument interest rate	5.70%
4.625% Subordinated notes due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2018
Debt instrument interest rate	4.625%
6.95% Subordinated notes due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2028
Debt instrument interest rate	6.95%
Lease financing debt due through 2016 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2016
Long-term debt weighted average interest rate	6.20%	5.44%
Federal Home Loan Bank [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2036
Long-term debt weighted average interest rate	1.09%	3.75%
Investment Fund Financing [Member]
Debt Instrument [Line Items]
Debt instrument maturity, year	2052
Long-term debt weighted average interest rate	2.01%	2.30%
Senior medium-term notes due through 2039 [Member]
Debt Instrument [Line Items]
Long-term debt weighted average interest rate	5.03%	3.91%