Loans and Related Allowance for Credit Losses (Home Equity and Residential Real Estate Credit Quality Indicators) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 237,013	$ 241,928
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	231	3,434
Financing receivable, originated in year one	3,280	2,000
Financing receivable, originated in year two	1,801	590
Financing receivable, originated in year three	534	830
Financing receivable, originated in year four	749	694
Prior	4,293	4,000
Revolving Loans	8,273	8,794
Revolving Loans Converted to Term	4,332	3,746
Total Loans	23,493	24,088
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	2,521	7,996
Financing receivable, originated in year one	7,311	4,158
Financing receivable, originated in year two	3,354	1,172
Financing receivable, originated in year three	974	1,942
Financing receivable, originated in year four	1,665	2,069
Prior	6,593	5,223
Total Loans	22,418	22,560
Greater than or equal to 780 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	127	2,019
Financing receivable, originated in year one	1,925	1,094
Financing receivable, originated in year two	960	311
Financing receivable, originated in year three	273	525
Financing receivable, originated in year four	467	449
Prior	2,640	2,467
Revolving Loans	5,148	5,382
Revolving Loans Converted to Term	1,844	1,480
Total Loans	13,384	13,727
Greater than or equal to 780 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1,409	5,425
Financing receivable, originated in year one	5,220	3,099
Financing receivable, originated in year two	2,411	814
Financing receivable, originated in year three	661	1,432
Financing receivable, originated in year four	1,206	1,538
Prior	3,564	2,551
Total Loans	14,471	14,859
720 to 779 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	84	1,028
Financing receivable, originated in year one	947	558
Financing receivable, originated in year two	505	153
Financing receivable, originated in year three	138	181
Financing receivable, originated in year four	164	145
Prior	865	777
Revolving Loans	1,950	2,137
Revolving Loans Converted to Term	1,084	941
Total Loans	5,737	5,920
720 to 779 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1,061	2,268
Financing receivable, originated in year one	1,767	820
Financing receivable, originated in year two	708	220
Financing receivable, originated in year three	182	340
Financing receivable, originated in year four	308	335
Prior	1,056	818
Total Loans	5,082	4,801
660 to 719 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	19	334
Financing receivable, originated in year one	346	273
Financing receivable, originated in year two	264	86
Financing receivable, originated in year three	83	84
Financing receivable, originated in year four	80	66
Prior	428	402
Revolving Loans	905	985
Revolving Loans Converted to Term	678	625
Total Loans	2,803	2,855
660 to 719 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	51	252
Financing receivable, originated in year one	267	161
Financing receivable, originated in year two	166	76
Financing receivable, originated in year three	81	98
Financing receivable, originated in year four	85	92
Prior	518	475
Total Loans	1,168	1,154
Less than 660 | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	1	52
Financing receivable, originated in year one	61	74
Financing receivable, originated in year two	71	39
Financing receivable, originated in year three	39	39
Financing receivable, originated in year four	37	33
Prior	350	345
Revolving Loans	255	277
Revolving Loans Converted to Term	628	620
Total Loans	1,442	1,479
Less than 660 | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		40
Financing receivable, originated in year one	43	48
Financing receivable, originated in year two	38	33
Financing receivable, originated in year three	23	31
Financing receivable, originated in year four	24	41
Prior	501	485
Total Loans	629	678
No FICO score available | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		1
Financing receivable, originated in year one	1	1
Financing receivable, originated in year two	1	1
Financing receivable, originated in year three	1	1
Financing receivable, originated in year four	1	1
Prior	10	9
Revolving Loans	15	13
Revolving Loans Converted to Term	98	80
Total Loans	127	107
No FICO score available | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		4
Financing receivable, originated in year one	6	2
Financing receivable, originated in year two	2	2
Financing receivable, originated in year three	2	3
Financing receivable, originated in year four	3	6
Prior	125	129
Total Loans	138	146
Government insured or guaranteed loans | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year		7
Financing receivable, originated in year one	8	28
Financing receivable, originated in year two	29	27
Financing receivable, originated in year three	25	38
Financing receivable, originated in year four	39	57
Prior	829	765
Total Loans	930	922
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	8	44
Financing receivable, originated in year two	41	18
Financing receivable, originated in year three	13	15
Financing receivable, originated in year four	10	9
Prior	73	88
Revolving Loans	471	580
Revolving Loans Converted to Term	254	279
Total Loans	870	1,041
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	4	52
Financing receivable, originated in year two	56	26
Financing receivable, originated in year three	23	42
Financing receivable, originated in year four	28	41
Prior	150	160
Total Loans	261	324
Greater than or equal to 80% to 100% | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	35	517
Financing receivable, originated in year one	253	320
Financing receivable, originated in year two	200	59
Financing receivable, originated in year three	39	42
Financing receivable, originated in year four	27	25
Prior	139	158
Revolving Loans	1,384	1,781
Revolving Loans Converted to Term	615	591
Total Loans	2,692	3,493
Greater than or equal to 80% to 100% | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	346	495
Financing receivable, originated in year one	142	422
Financing receivable, originated in year two	274	127
Financing receivable, originated in year three	70	156
Financing receivable, originated in year four	113	124
Prior	328	307
Total Loans	1,273	1,631
Less than 80% | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	196	2,909
Financing receivable, originated in year one	3,019	1,636
Financing receivable, originated in year two	1,560	513
Financing receivable, originated in year three	482	773
Financing receivable, originated in year four	712	660
Prior	4,081	3,754
Revolving Loans	6,418	6,433
Revolving Loans Converted to Term	3,463	2,876
Total Loans	19,931	19,554
Less than 80% | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, originated in current year	2,175	7,491
Financing receivable, originated in year one	7,157	3,656
Financing receivable, originated in year two	2,995	992
Financing receivable, originated in year three	856	1,706
Financing receivable, originated in year four	1,485	1,847
Prior	5,286	3,991
Total Loans	$ 19,954	$ 19,683