Investment Securities - Schedule of Available-for-Sale Securities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Non-Agency | RMBS
Schedule of Available-for-sale Securities [Line Items]
Non-credit OTTI losses related to non-agency RMBS	$ 8	$ 12
Other Asset-backed Securities Portfolio | Collateralized by Credit Card Loans
Schedule of Available-for-sale Securities [Line Items]
Percentage of portfolio	55.00%	65.00%
Other Asset-backed Securities Portfolio | Auto Dealer Floor Plan Inventory Loans and Leases
Schedule of Available-for-sale Securities [Line Items]
Percentage of portfolio	16.00%	15.00%
Other Asset-backed Securities Portfolio | Securities Rated AAA or Equivalent
Schedule of Available-for-sale Securities [Line Items]
Percentage of portfolio	89.00%	87.00%