Derivatives - Gains/(Losses) on Derivatives Associated with Mortgage Banking Hedges (Details) - Mortgage Banking Hedges - Hedged Items - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Option contracts written
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	$ (3)	$ 7	$ (12)	$ 7
Forward contracts purchased
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) on derivative instruments	$ (2)	$ (10)	$ 10	$ (10)

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959

Name:	us-gaap_GainLossOnDerivativeInstrumentsNetPretax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration