Fair Value Measures - Quantitative Information about Recurring Level 3 Fair Value Financial Instruments (Details) $ in Millions	Sep. 30, 2023 USD ($) constant_default_rate_per_loan	Dec. 31, 2022 USD ($)
Assets:
Mortgage servicing rights | $	$ 1,135	$ 1,033
Recurring
Assets:
Mortgage servicing rights | $	1,135	1,033
Recurring | Rate lock commitments
Liabilities:
Rate lock commitments (net) | $	12	10
Significant Unobservable Inputs (Level 3) | Recurring
Assets:
Mortgage servicing rights | $	1,135	1,033
Significant Unobservable Inputs (Level 3) | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights | $	1,135
Significant Unobservable Inputs (Level 3) | Recurring | Valuation Technique, Discounted Cash Flow | Private Label CMOs
Assets:
Mortgage servicing rights | $	32
Significant Unobservable Inputs (Level 3) | Recurring | Rate lock commitments
Liabilities:
Rate lock commitments (net) | $	12	$ 10
Significant Unobservable Inputs (Level 3) | Recurring | Rate lock commitments | Valuation Technique, Consensus Pricing Model
Liabilities:
Rate lock commitments (net) | $	$ (6)
Significant Unobservable Inputs (Level 3) | Option adjusted spread | Minimum | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	0.052
Significant Unobservable Inputs (Level 3) | Option adjusted spread | Maximum | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	0.217
Significant Unobservable Inputs (Level 3) | Option adjusted spread | Weighted average | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	0.056
Significant Unobservable Inputs (Level 3) | Constant prepayment rate | Minimum | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	0
Significant Unobservable Inputs (Level 3) | Constant prepayment rate | Maximum | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	0.100
Significant Unobservable Inputs (Level 3) | Constant prepayment rate | Weighted average | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	0.073
Significant Unobservable Inputs (Level 3) | Weighted average cost to service per loan | Minimum | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	65
Significant Unobservable Inputs (Level 3) | Weighted average cost to service per loan | Maximum | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	90
Significant Unobservable Inputs (Level 3) | Weighted average cost to service per loan | Weighted average | Recurring | Valuation Technique, Discounted Cash Flow | Residential Mortgage Servicing Rights
Assets:
Mortgage servicing rights, measurement input	69
Significant Unobservable Inputs (Level 3) | Origination pull-through rate | Recurring | Valuation Technique, Consensus Pricing Model
Liabilities:
Rate lock commitments (net), measurement input	0.7110
Significant Unobservable Inputs (Level 3) | Constant default rates | Minimum | Recurring | Private Label CMOs
Liabilities:
Rate lock commitments (net), measurement input	0.0010
Significant Unobservable Inputs (Level 3) | Constant default rates | Maximum | Recurring | Private Label CMOs
Liabilities:
Rate lock commitments (net), measurement input	0.0030
Significant Unobservable Inputs (Level 3) | Weighted average life | Minimum | Recurring | Private Label CMOs
Liabilities:
Rate lock commitments (net), measurement input	0.082
Significant Unobservable Inputs (Level 3) | Weighted average life | Maximum | Recurring | Private Label CMOs
Liabilities:
Rate lock commitments (net), measurement input	0.119