Loans and Related Allowance for Credit Losses (Home Equity and Residential Real Estate Credit Quality Indicators) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 294,704	$ 241,928
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	235	3,434
Financing receivable, originated in year one	3,072	2,000
Financing receivable, originated in year two	1,618	590
Financing receivable, originated in year three	485	830
Financing receivable, originated in year four	682	694
Prior	4,009	4,000
Revolving Loans	10,168	8,794
Revolving Loans Converted to Term	4,905	3,746
Total Loans	25,174	24,088
Home equity | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	7
Financing receivable, originated in year one	10
Financing receivable, originated in year two	9
Financing receivable, originated in year three	7
Financing receivable, originated in year four	4
Prior	113
Revolving Loans	2,263
Revolving Loans Converted to Term	5
Total Loans	2,418
Home equity | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	228
Financing receivable, originated in year one	3,062
Financing receivable, originated in year two	1,609
Financing receivable, originated in year three	478
Financing receivable, originated in year four	678
Prior	3,896
Revolving Loans	7,905
Revolving Loans Converted to Term	4,900
Total Loans	22,756
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	8,215	7,996
Financing receivable, originated in year one	10,489	4,158
Financing receivable, originated in year two	4,360	1,172
Financing receivable, originated in year three	1,464	1,942
Financing receivable, originated in year four	2,143	2,069
Prior	10,175	5,223
Total Loans	36,846	22,560
Residential real estate | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	6,306
Financing receivable, originated in year one	6,647
Financing receivable, originated in year two	2,774
Financing receivable, originated in year three	790
Financing receivable, originated in year four	1,425
Prior	5,870
Total Loans	23,812
Residential real estate | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1,909
Financing receivable, originated in year one	3,842
Financing receivable, originated in year two	1,586
Financing receivable, originated in year three	674
Financing receivable, originated in year four	718
Prior	4,305
Total Loans	13,034
Greater than or equal to 780 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	132	2,019
Financing receivable, originated in year one	1,905	1,094
Financing receivable, originated in year two	897	311
Financing receivable, originated in year three	248	525
Financing receivable, originated in year four	436	449
Prior	2,469	2,467
Revolving Loans	6,028	5,382
Revolving Loans Converted to Term	2,310	1,480
Total Loans	14,425	13,727
Greater than or equal to 780 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	4,691	5,425
Financing receivable, originated in year one	7,211	3,099
Financing receivable, originated in year two	2,922	814
Financing receivable, originated in year three	832	1,432
Financing receivable, originated in year four	1,361	1,538
Prior	5,170	2,551
Total Loans	22,187	14,859
720 to 779 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	78	1,028
Financing receivable, originated in year one	818	558
Financing receivable, originated in year two	434	153
Financing receivable, originated in year three	125	181
Financing receivable, originated in year four	143	145
Prior	779	777
Revolving Loans	2,469	2,137
Revolving Loans Converted to Term	1,239	941
Total Loans	6,085	5,920
720 to 779 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	2,667	2,268
Financing receivable, originated in year one	2,213	820
Financing receivable, originated in year two	870	220
Financing receivable, originated in year three	287	340
Financing receivable, originated in year four	422	335
Prior	1,838	818
Total Loans	8,297	4,801
660 to 719 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	20	334
Financing receivable, originated in year one	297	273
Financing receivable, originated in year two	222	86
Financing receivable, originated in year three	72	84
Financing receivable, originated in year four	71	66
Prior	410	402
Revolving Loans	1,168	985
Revolving Loans Converted to Term	690	625
Total Loans	2,950	2,855
660 to 719 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	252	252
Financing receivable, originated in year one	530	161
Financing receivable, originated in year two	299	76
Financing receivable, originated in year three	163	98
Financing receivable, originated in year four	143	92
Prior	913	475
Total Loans	2,300	1,154
Less than 660 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	3	52
Financing receivable, originated in year one	50	74
Financing receivable, originated in year two	64	39
Financing receivable, originated in year three	38	39
Financing receivable, originated in year four	31	33
Prior	339	345
Revolving Loans	412	277
Revolving Loans Converted to Term	575	620
Total Loans	1,512	1,479
Less than 660 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	29	40
Financing receivable, originated in year one	110	48
Financing receivable, originated in year two	101	33
Financing receivable, originated in year three	90	31
Financing receivable, originated in year four	99	41
Prior	872	485
Total Loans	1,301	678
No FICO score available | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	2	1
Financing receivable, originated in year one	2	1
Financing receivable, originated in year two	1	1
Financing receivable, originated in year three	2	1
Financing receivable, originated in year four	1	1
Prior	12	9
Revolving Loans	91	13
Revolving Loans Converted to Term	91	80
Total Loans	202	107
No FICO score available | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	575	4
Financing receivable, originated in year one	411	2
Financing receivable, originated in year two	124	2
Financing receivable, originated in year three	57	3
Financing receivable, originated in year four	73	6
Prior	579	129
Total Loans	1,819	146
Government insured or guaranteed loans | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1	7
Financing receivable, originated in year one	14	28
Financing receivable, originated in year two	44	27
Financing receivable, originated in year three	35	38
Financing receivable, originated in year four	45	57
Prior	803	765
Total Loans	942	922
Government insured or guaranteed loans | Residential real estate | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1
Financing receivable, originated in year one	4
Financing receivable, originated in year two	14
Financing receivable, originated in year three	11
Financing receivable, originated in year four	10
Prior	37
Total Loans	77
Government insured or guaranteed loans | Residential real estate | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in year one	10
Financing receivable, originated in year two	29
Financing receivable, originated in year three	24
Financing receivable, originated in year four	35
Prior	767
Total Loans	865
Greater than 100% | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		8
Financing receivable, originated in year one		44
Financing receivable, originated in year two		18
Financing receivable, originated in year three		15
Financing receivable, originated in year four		9
Prior		88
Revolving Loans		580
Revolving Loans Converted to Term		279
Total Loans		1,041
Greater than 100% | Home equity | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Prior	3
Revolving Loans	68
Total Loans	71
Greater than 100% | Home equity | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in year one	20
Financing receivable, originated in year two	32
Financing receivable, originated in year three	9
Financing receivable, originated in year four	7
Prior	100
Revolving Loans	418
Revolving Loans Converted to Term	203
Total Loans	789
Greater than 100% | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		3
Financing receivable, originated in year one		52
Financing receivable, originated in year two		26
Financing receivable, originated in year three		42
Financing receivable, originated in year four		41
Prior		160
Total Loans		324
Greater than 100% | Residential real estate | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	11
Financing receivable, originated in year one	24
Financing receivable, originated in year two	3
Financing receivable, originated in year three	2
Financing receivable, originated in year four	4
Prior	23
Total Loans	67
Greater than 100% | Residential real estate | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1
Financing receivable, originated in year one	16
Financing receivable, originated in year two	58
Financing receivable, originated in year three	18
Financing receivable, originated in year four	29
Prior	194
Total Loans	316
Greater than or equal to 80% to 100% | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		517
Financing receivable, originated in year one		320
Financing receivable, originated in year two		59
Financing receivable, originated in year three		42
Financing receivable, originated in year four		25
Prior		158
Revolving Loans		1,781
Revolving Loans Converted to Term		591
Total Loans		3,493
Greater than or equal to 80% to 100% | Home equity | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1
Financing receivable, originated in year one	5
Financing receivable, originated in year two	3
Financing receivable, originated in year three	2
Financing receivable, originated in year four	1
Prior	16
Revolving Loans	578
Revolving Loans Converted to Term	1
Total Loans	607
Greater than or equal to 80% to 100% | Home equity | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	23
Financing receivable, originated in year one	176
Financing receivable, originated in year two	145
Financing receivable, originated in year three	28
Financing receivable, originated in year four	19
Prior	119
Revolving Loans	1,081
Revolving Loans Converted to Term	548
Total Loans	2,139
Greater than or equal to 80% to 100% | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		495
Financing receivable, originated in year one		422
Financing receivable, originated in year two		127
Financing receivable, originated in year three		156
Financing receivable, originated in year four		124
Prior		307
Total Loans		1,631
Greater than or equal to 80% to 100% | Residential real estate | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	635
Financing receivable, originated in year one	1,407
Financing receivable, originated in year two	612
Financing receivable, originated in year three	293
Financing receivable, originated in year four	286
Prior	664
Total Loans	3,897
Greater than or equal to 80% to 100% | Residential real estate | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	727
Financing receivable, originated in year one	157
Financing receivable, originated in year two	160
Financing receivable, originated in year three	44
Financing receivable, originated in year four	63
Prior	248
Total Loans	1,399
Less than 80% | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		2,909
Financing receivable, originated in year one		1,636
Financing receivable, originated in year two		513
Financing receivable, originated in year three		773
Financing receivable, originated in year four		660
Prior		3,754
Revolving Loans		6,433
Revolving Loans Converted to Term		2,876
Total Loans		19,554
Less than 80% | Home equity | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	6
Financing receivable, originated in year one	5
Financing receivable, originated in year two	6
Financing receivable, originated in year three	5
Financing receivable, originated in year four	3
Prior	90
Revolving Loans	1,572
Revolving Loans Converted to Term	3
Total Loans	1,690
Less than 80% | Home equity | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	205
Financing receivable, originated in year one	2,866
Financing receivable, originated in year two	1,432
Financing receivable, originated in year three	441
Financing receivable, originated in year four	652
Prior	3,677
Revolving Loans	6,406
Revolving Loans Converted to Term	4,149
Total Loans	19,828
Less than 80% | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		7,491
Financing receivable, originated in year one		3,656
Financing receivable, originated in year two		992
Financing receivable, originated in year three		1,706
Financing receivable, originated in year four		1,847
Prior		3,991
Total Loans		$ 19,683
Less than 80% | Residential real estate | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1,158
Financing receivable, originated in year one	2,094
Financing receivable, originated in year two	843
Financing receivable, originated in year three	330
Financing receivable, originated in year four	414
Prior	3,581
Total Loans	8,420
Less than 80% | Residential real estate | Financial Asset Originated
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	5,578
Financing receivable, originated in year one	6,464
Financing receivable, originated in year two	2,527
Financing receivable, originated in year three	704
Financing receivable, originated in year four	1,298
Prior	4,661
Total Loans	21,232
No LTV ratio available | Home equity | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Prior	4
Revolving Loans	45
Revolving Loans Converted to Term	1
Total Loans	50
No LTV ratio available | Residential real estate | Acquired Loans Portfolio
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	104
Financing receivable, originated in year one	313
Financing receivable, originated in year two	114
Financing receivable, originated in year three	38
Financing receivable, originated in year four	4
Total Loans	$ 573