Employee Benefit Plans - Obligations and Funded Status, Additional Information (Details) - USD ($) $ in Millions		12 Months Ended
	Jun. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		3.30%	3.30%	3.30%
Fair value of plan assets had fair value of rabbi trusts been included		$ 4,075	$ 3,483
Funded status of plan had fair value of rabbi trust assets been included		$ 423	$ (517)
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate		3.33%	4.35%
Defined Benefit Plan, Benefit Obligation		$ 4,498	$ 4,000	$ 4,376
Transferred pension obligation	$ 1,600
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	$ (750)
Assets held in rabbi trusts and designated for the non-qualified pension plans		161	139
Cash | Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation		420	412
Change in Assumptions for Defined Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation, Period Increase (Decrease)		$ 508	$ 281
Discount rate		3.33%	4.35%	3.73%