Employee Benefit Plans (Reconciliation of Changes in Projected Benefit Obligation and Change in Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, beginning balance	$ 6,073
Fair value of plan assets, end balance	6,788	$ 6,073
Pension Plans | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	5,370	5,117
Projected benefit obligation at beginning of year	5,174	4,887
Service cost	133	122	$ 115
Interest cost	139	160	186
Amendments	(4)
Actuarial (gains)/losses and changes in assumptions	(88)	306
Benefits paid	(320)	(301)
Projected benefit obligation from BBVA acquisition	389
Projected benefit obligation at end of year	5,423	5,174	4,887
Fair value of plan assets, beginning balance	6,073	5,654
Actual return on plan assets	670	720
Benefits paid	(320)	(301)
Fair value of plan assets from BBVA acquisition	365
Fair value of plan assets, end balance	6,788	6,073	5,654
Funded status	1,365	899
Noncurrent asset	1,365	899
Net amount recognized on the consolidated balance sheet	1,365	899
Prior service cost (credit)	17	25
Net actuarial loss (gain)	(186)	299
Amount recognized in AOCI	(169)	324
Pension Plans | Nonqualified Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	272	258
Projected benefit obligation at beginning of year	263	265
Service cost	4	3	3
Interest cost	6	8	10
Actuarial (gains)/losses and changes in assumptions	(4)	17
Benefits paid	(21)	(30)
Projected benefit obligation from BBVA acquisition	32
Projected benefit obligation at end of year	280	263	265
Fair value of plan assets, beginning balance
Employer contribution	21	30
Benefits paid	(21)	(30)
Fair value of plan assets, end balance
Funded status	(280)	(263)
Current liability	(25)	(25)
Noncurrent liability	(255)	(238)
Net amount recognized on the consolidated balance sheet	(280)	(263)
Net actuarial loss (gain)	80	90
Amount recognized in AOCI	80	90
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at beginning of year	337	333
Service cost	4	4	4
Interest cost	8	11	13
Actuarial (gains)/losses and changes in assumptions	(11)	11
Participant contributions	3	3
Federal Medicare subsidy on benefits paid	1
Benefits paid	(25)	(25)
Projected benefit obligation from BBVA acquisition	9
Projected benefit obligation at end of year	326	337	333
Fair value of plan assets, beginning balance	262	247
Actual return on plan assets	2	14
Employer contribution	20	23
Participant contributions	3	3
Federal Medicare subsidy on benefits paid	1
Benefits paid	(25)	(25)
Fair value of plan assets, end balance	263	262	$ 247
Funded status	(63)	(75)
Current liability	(2)	(2)
Noncurrent liability	(61)	(73)
Net amount recognized on the consolidated balance sheet	(63)	(75)
Prior service cost (credit)	1	2
Net actuarial loss (gain)	(2)	4
Amount recognized in AOCI	$ (1)	$ 6