Benefit Plans - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discretionary contributions		$ 305,000,000
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent		50.00%
Defined Contribution Plan, Minimum Age of Employees Covered		21 years
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Compensation, Maximum		6.00%
Defined Contribution Plan, Employer Contribution Expense		$ 152,000,000	$ 141,000,000	$ 133,000,000
Other Liabilities		12,236,000,000	5,433,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Liabilities		116,000,000
Alternative Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		$ 341,000,000	$ 274,000,000
Subsequent Event
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected long-term rate of return on plan assets	6.90%