Employee Benefit Plans - Schedule of Changes in Benefit Obligation and Fair Value of Plan Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 30, 2016	Dec. 31, 2018	Dec. 31, 2017
Change in Projected Benefit Obligation:
Workforce Reduction Program/Curtailment and Post-retirement Plan Amendment	$ (102,000,000)
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Plan Year	2,833,000,000
Non-qualified Employer Contributions	0	$ 0	$ 250,000,000
Fair Value of Plan Assets at End of Plan Year	2,431,000,000	2,833,000,000
Capitalized service costs	4,000,000
Pension Benefits
Actuarial Present Value of Benefit Obligation
Accumulated Benefit Obligation				$ 2,623,000,000	$ 2,873,000,000
Projected Benefit Obligation	3,002,000,000	2,871,000,000	2,871,000,000	2,758,000,000	3,002,000,000
Change in Projected Benefit Obligation:
Projected Benefit Obligation at Beginning of Plan Year	3,002,000,000	2,871,000,000
Service Cost	36,000,000	36,000,000
Interest Cost	92,000,000	92,000,000	119,000,000
Plan Participants' Contributions	0	0
Workforce Reduction Program/Curtailment and Post-retirement Plan Amendment	0	58,000,000
Actuarial (Gain) Loss	(173,000,000)	163,000,000
Benefits Paid	(199,000,000)	(218,000,000)
Benefit Obligation at End of Plan Year	2,758,000,000	3,002,000,000	2,871,000,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Plan Year	2,833,000,000	2,539,000,000
Actual Return on Plan Assets (Loss) Gain	(220,000,000)	467,000,000
Plan Participants' Contributions	0	0
Benefits Paid	(199,000,000)	(218,000,000)
Fair Value of Plan Assets at End of Plan Year	2,431,000,000	2,833,000,000	2,539,000,000
Funded Status at End of Plan Year				(327,000,000)	(169,000,000)
Pension Benefits | Nonqualified Plan
Change in Plan Assets:
Non-qualified Employer Contributions	17,000,000	45,000,000
Post-retirement Benefits
Actuarial Present Value of Benefit Obligation
Projected Benefit Obligation	250,000,000	274,000,000	274,000,000	118,000,000	250,000,000
Change in Projected Benefit Obligation:
Projected Benefit Obligation at Beginning of Plan Year	250,000,000	274,000,000
Service Cost	2,000,000	2,000,000
Interest Cost	7,000,000	7,000,000	12,000,000
Plan Participants' Contributions	5,000,000	7,000,000
Workforce Reduction Program/Curtailment and Post-retirement Plan Amendment	(102,000,000)	13,000,000
Actuarial (Gain) Loss	(10,000,000)	(17,000,000)
Benefits Paid	(34,000,000)	(36,000,000)
Benefit Obligation at End of Plan Year	118,000,000	250,000,000	274,000,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Plan Year	0	0
Actual Return on Plan Assets (Loss) Gain	0	0
Plan Participants' Contributions	4,000,000	7,000,000
Benefits Paid	(34,000,000)	(36,000,000)
Fair Value of Plan Assets at End of Plan Year	0	0	$ 0
Funded Status at End of Plan Year				$ (118,000,000)	$ (250,000,000)
Post-retirement Benefits | Nonqualified Plan
Change in Plan Assets:
Non-qualified Employer Contributions	$ 30,000,000	$ 29,000,000