Loans and Related Allowance for Credit Losses (Home Equity and Residential Real Estate Credit Quality Indicators) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 249,279	$ 239,843
Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	2,643
Financing receivable, originated in 2019	2,257
Financing receivable, originated in 2018	660
Financing receivable, originated in 2017	921
Financing receivable, originated in 2016	768
Prior	4,394
Revolving Loans	9,233
Revolving Loans Converted to Term	3,663
Total Loans	24,539	25,085
Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	6,194
Financing receivable, originated in 2019	4,883
Financing receivable, originated in 2018	1,417
Financing receivable, originated in 2017	2,290
Financing receivable, originated in 2016	2,389
Prior	5,713
Total Loans	22,886	21,821
FICO Score- Greater than 660 [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	2,580
Financing receivable, originated in 2019	2,156
Financing receivable, originated in 2018	605
Financing receivable, originated in 2017	867
Financing receivable, originated in 2016	725
Prior	3,955
Revolving Loans	8,818
Revolving Loans Converted to Term	2,846
Total Loans	22,552	22,245
FICO Score- Greater than 660 [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	6,151
Financing receivable, originated in 2019	4,813
Financing receivable, originated in 2018	1,362
Financing receivable, originated in 2017	2,215
Financing receivable, originated in 2016	2,272
Prior	4,295
Total Loans	21,108	19,341
FICO Score- Less than or equal to 660 [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	62
Financing receivable, originated in 2019	101
Financing receivable, originated in 2018	54
Financing receivable, originated in 2017	53
Financing receivable, originated in 2016	42
Prior	429
Revolving Loans	402
Revolving Loans Converted to Term	732
Total Loans	1,875	2,019
FICO Score- Less than or equal to 660 [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	36
Financing receivable, originated in 2019	45
Financing receivable, originated in 2018	30
Financing receivable, originated in 2017	37
Financing receivable, originated in 2016	62
Prior	567
Total Loans	777	569
No FICO Score Available [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	1
Financing receivable, originated in 2018	1
Financing receivable, originated in 2017	1
Financing receivable, originated in 2016	1
Prior	10
Revolving Loans	13
Revolving Loans Converted to Term	85
Total Loans	112	278
No FICO Score Available [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	2
Financing receivable, originated in 2019	2
Financing receivable, originated in 2018	2
Financing receivable, originated in 2017	4
Financing receivable, originated in 2016	6
Prior	134
Total Loans	150	151
Purchased Impaired Loans [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans		543
Purchased Impaired Loans [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans		1,176
Loans Insured or Guaranteed by US Government Authorities [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	5
Financing receivable, originated in 2019	23
Financing receivable, originated in 2018	23
Financing receivable, originated in 2017	34
Financing receivable, originated in 2016	49
Prior	717
Total Loans	851	584
LTV Greater Than Or Equal To 100 Percent [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	5
Financing receivable, originated in 2019	41
Financing receivable, originated in 2018	18
Financing receivable, originated in 2017	17
Financing receivable, originated in 2016	10
Prior	100
Revolving Loans	605
Revolving Loans Converted to Term	309
Total Loans	1,105	1,243
LTV Greater Than Or Equal To 100 Percent [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2019	34
Financing receivable, originated in 2018	33
Financing receivable, originated in 2017	49
Financing receivable, originated in 2016	49
Prior	189
Total Loans	354	333
LTV Greater Than Or Equal To 90 Percent To Less Than 100 Percent [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	29
Financing receivable, originated in 2019	95
Financing receivable, originated in 2018	21
Financing receivable, originated in 2017	15
Financing receivable, originated in 2016	8
Prior	69
Revolving Loans	687
Revolving Loans Converted to Term	226
Total Loans	1,150	1,047
LTV Greater Than Or Equal To 90 Percent To Less Than 100 Percent [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	15
Financing receivable, originated in 2019	69
Financing receivable, originated in 2018	32
Financing receivable, originated in 2017	54
Financing receivable, originated in 2016	37
Prior	114
Total Loans	321	340
LTV Less Than 90 Percent [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	2,609
Financing receivable, originated in 2019	2,121
Financing receivable, originated in 2018	621
Financing receivable, originated in 2017	889
Financing receivable, originated in 2016	750
Prior	4,225
Revolving Loans	7,941
Revolving Loans Converted to Term	3,128
Total Loans	22,284	22,068
LTV Less Than 90 Percent [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in 2020	6,174
Financing receivable, originated in 2019	4,757
Financing receivable, originated in 2018	1,329
Financing receivable, originated in 2017	2,153
Financing receivable, originated in 2016	2,254
Prior	4,693
Total Loans	$ 21,360	19,305
No LTV Ratio Available [Member] | Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans		184
No LTV Ratio Available [Member] | Residential Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans		$ 83