Employee Benefit Plans - Obligations and Funded Status, Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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	$ 4,549	$ 4,075
Funded status of plan had fair value of rabbi trust assets been included	$ 326	$ (423)
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	2.65%	3.33%
Defined Benefit Plan, Benefit Obligation	$ 4,875	$ 4,498	$ 4,000
Assets held in rabbi trusts and designated for the non-qualified pension plans	186	161
Cash Balance Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	443	420
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)	$ 434	$ 508
Discount rate	2.65%	3.33%	4.35%