Employee Benefit Plans - Schedule of Changes in Benefit Obligation and Fair Value of Plan Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Change in Projected Benefit Obligation:
Post-retirement Plan Amendment		$ 102,000,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Plan Year	$ 2,431,000,000
Non-qualified Employer Contributions	0	0	$ 0
Fair Value of Plan Assets at End of Plan Year	2,825,000,000	2,431,000,000
Capitalized service costs	3,000,000	3,000,000
Pension Benefits
Actuarial Present Value of Benefit Obligation
Accumulated Benefit Obligation				$ 2,963,000,000	$ 2,623,000,000
Projected Benefit Obligation	2,758,000,000	2,758,000,000	3,002,000,000	3,122,000,000	2,758,000,000
Change in Projected Benefit Obligation:
Projected Benefit Obligation at Beginning of Plan Year	2,758,000,000	3,002,000,000
Service Cost	34,000,000	36,000,000
Interest Cost	103,000,000	92,000,000	92,000,000
Plan Participants' Contributions	0	0
Post-retirement Plan Amendment	0	0
Actuarial Loss (Gain)	418,000,000	(173,000,000)
Benefits Paid	(191,000,000)	(199,000,000)
Benefit Obligation at End of Plan Year	3,122,000,000	2,758,000,000	3,002,000,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Plan Year	2,431,000,000	2,833,000,000
Actual Return on Plan Assets Gain (Loss)	568,000,000	(220,000,000)
Plan Participants' Contributions	0	0
Benefits Paid	(191,000,000)	(199,000,000)
Fair Value of Plan Assets at End of Plan Year	2,825,000,000	2,431,000,000	2,833,000,000
Funded Status at End of Plan Year				(297,000,000)	(327,000,000)
Pension Benefits | Nonqualified Plan
Change in Plan Assets:
Non-qualified Employer Contributions	17,000,000	17,000,000
Post-retirement Benefits
Actuarial Present Value of Benefit Obligation
Projected Benefit Obligation	118,000,000	118,000,000	250,000,000	117,000,000	118,000,000
Change in Projected Benefit Obligation:
Projected Benefit Obligation at Beginning of Plan Year	118,000,000	250,000,000
Service Cost	1,000,000	2,000,000
Interest Cost	2,000,000	7,000,000	7,000,000
Plan Participants' Contributions	7,000,000	5,000,000
Post-retirement Plan Amendment	0	(102,000,000)
Actuarial Loss (Gain)	22,000,000	(10,000,000)
Benefits Paid	(33,000,000)	(34,000,000)
Benefit Obligation at End of Plan Year	117,000,000	118,000,000	250,000,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Plan Year	0	0
Actual Return on Plan Assets Gain (Loss)	0	0
Plan Participants' Contributions	7,000,000	4,000,000
Benefits Paid	(33,000,000)	(34,000,000)
Fair Value of Plan Assets at End of Plan Year	0	0	$ 0
Funded Status at End of Plan Year				$ (117,000,000)	$ (118,000,000)
Post-retirement Benefits | Nonqualified Plan
Change in Plan Assets:
Non-qualified Employer Contributions	$ 26,000,000	$ 30,000,000