Acquisitions and Discontinued Operations - Principal and Fair Value Amounts for Trust Loans at Fair Value, Portfolio Loans at Fair Value, and Portfolio Loans at Carrying Value (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Principal [Member] | Trust [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	$ 25	$ 25	$ 33
Loans placed on nonaccrual status	10	12	13
Principal [Member] | Portfolio [Member] | Fair Value [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	7	8	5
Loans placed on nonaccrual status
Principal [Member] | Portfolio [Member] | Carrying Amount [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	32	35	41
Loans placed on nonaccrual status	8	10	3
Fair Value [Member] | Trust [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	25	25	32
Loans placed on nonaccrual status	10	12	12
Fair Value [Member] | Portfolio [Member] | Fair Value [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accruing loans past due 90 days or more	7	8	5
Loans placed on nonaccrual status