Employee Benefit Plans (Net Periodic Defined Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020		Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Net periodic defined benefit credit				$ (61)	$ (41)
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 8	[1]	29	24	[1]
Interest Cost	16	18	[1]	46	53	[1]
Expected return on plan assets	(51)	(47)	[1]	(152)	(138)	[1]
Amortization of prior service credit	(5)	(5)	[1]	(14)	(15)	[1]
Amortization of net loss	7	9	[1]	22	28	[1]
Total other components of net benefit credit	(33)	(25)	[1]	(98)	(72)	[1]
Net periodic defined benefit credit	(23)	(17)	[1]	(69)	(48)	[1]
Non-Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0		1	1
Interest Cost	2	2		5	6
Amortization of prior service credit	(2)	(2)		(5)	(6)
Amortization of net loss	3	3		8	7
Total other components of net benefit credit	3	3		8	7
Net periodic defined benefit credit	3	3		9	8
Postretirement Benefit Plan
Defined Benefit Plan Disclosure [Line Items]
Interest Cost	1	1		1	1
Expected return on plan assets	(1)	(1)		(2)	(2)
Net periodic defined benefit credit	$ 0	$ 0		$ (1)	$ (1)

[1] Recast to reflect the retrospective application of the Corporation's election to change the accounting method for certain components of defined pension benefit credit, effective January 1, 2021. For the three months ended September 30, 2020, expected return on plan assets increased $4 million and amortization of net loss was reduced by $4 million, resulting in an increase of $8 million to total other components of net benefit credit. For the nine months ended September 30, 2020, expected return on plan assets increased $10 million and amortization of net loss was reduced by $12 million, resulting in an increase of $22 million to total other components of net benefit credit. Refer to Note 1 for further information.