Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Abstract]
Deferred tax assets related to state net operating loss carryforwards	$ 18	$ 22
Operating loss carryforwards valuation allowances	19	19
Operating loss carryforwards expiration date	Dec. 31, 2034
Accrued interest liabilities, net of the related tax benefits	1	1
Retained earnings included allocation of earnings for bad debt deductions of former thrift subsidiaries	$ 157	$ 157