Estimated Amortization Expense (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Expected Amortization Expense
Future Amortization Expense, Year One	$ 215
Future Amortization Expense, Year Two	230
Future Amortization Expense, Year Three	182
Future Amortization Expense, Year Four	148
Future Amortization Expense, Year Five	119
Servicing Rights
Expected Amortization Expense
Future Amortization Expense, Year One	209
Future Amortization Expense, Year Two	225
Future Amortization Expense, Year Three	180
Future Amortization Expense, Year Four	146
Future Amortization Expense, Year Five	117
Other Intangible Assets
Expected Amortization Expense
Future Amortization Expense, Year One	6
Future Amortization Expense, Year Two	5
Future Amortization Expense, Year Three	2
Future Amortization Expense, Year Four	2
Future Amortization Expense, Year Five	$ 2