Commitments (Activity in Reserve for Representation and Warranty Provisions) (Detail) - Residential Mortgage - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Valuation And Qualifying Accounts Disclosure
Balance, beginning of period	$ 6	$ 9
Net (reductions) additions to the reserve	2	(1)
Balance, end of period	$ 8	$ 8

Amount of increase (decrease) in valuation and qualifying accounts and reserves.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

Name:	us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration