Summary of Significant Accounting Policies and New Accounting Pronouncements - Calculation of Lifetime ECL (Details)	12 Months Ended
	Dec. 31, 2021 scenario
Financing Receivable, Allowance for Credit Loss [Line Items]
Number of forward-looking economic scenarios	3
Reasonable and supportable forecast period for consensus economic scenarios	2 years
Reversion period for average historical values	20 years
Reversion period for most assumption variables	3 years
Consumer loans: | Residential mortgages | Minimum
Financing Receivable, Allowance for Credit Loss [Line Items]
Measurement input (in percent)	0.20
Consumer loans: | Residential mortgages | Maximum
Financing Receivable, Allowance for Credit Loss [Line Items]
Measurement input (in percent)	0.40
Consumer loans: | Home Equity Mortgages | Minimum
Financing Receivable, Allowance for Credit Loss [Line Items]
Measurement input (in percent)	0.70
Consumer loans: | Home Equity Mortgages | Maximum
Financing Receivable, Allowance for Credit Loss [Line Items]
Measurement input (in percent)	1