Summary of Significant Accounting Policies and New Accounting Pronouncements - Calculation of Lifetime ECL (Details)	12 Months Ended
	Dec. 31, 2020 scenario	Jan. 01, 2020 scenario
Financing Receivable, Allowance for Credit Loss [Line Items]
Number of forward-looking economic scenarios	4	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 [Member] | Residential Mortgage [Member] | Measurement Input, Loss Severity Rates [Member] | Minimum [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0.20
Consumer Loans [Member] | Residential Mortgage [Member] | Measurement Input, Loss Severity Rates [Member] | Maximum [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0.40
Consumer Loans [Member] | Home Equity Mortgages [Member] | Measurement Input, Loss Severity Rates [Member] | Minimum [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	0.70
Consumer Loans [Member] | Home Equity Mortgages [Member] | Measurement Input, Loss Severity Rates [Member] | Maximum [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans	1