Income Taxes (Income Taxes - Additional Information) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Deferred tax assets related to state net operating loss carryforwards	$ 9	$ 9
State net operating loss carryforwards specific valuation allowances	$ 27	25
State net operating loss carryforwards expiration date	Dec. 31, 2037
Deferred tax assets related to foreign tax credit carryforward	$ 2	3
Foreign tax credit carryforward expiration date	Dec. 31, 2025
Accrued interest liabilities, net of the related tax benefits	$ 3	1
Allocation of earnings for bad debt deductions of former thrift subsidiaries included in retained earnings	157	157
Interest expense recognized in connection with income taxes	2	$ 1
Remeasurement of leveraged leases	27
Remeasurment of deferred tax assets and liabilities	$ 220