Benefit Plans, Pension Plan Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Limited Partnership Investments [Abstract]
Percentage of carrying value of investments employing hedge fund strategies	66.00%	75.00%
Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	$ 0	$ 0
Hedge Funds, Equity Related
Limited Partnership Investments [Abstract]
Percentage of carrying value of investments in limited partnerships	76.00%
Hedge Funds, Multi-Strategy Approach Hedge Funds
Limited Partnership Investments [Abstract]
Percentage of carrying value of investments in limited partnerships	20.00%
Hedge Funds, Distressed Investments
Limited Partnership Investments [Abstract]
Percentage of carrying value of investments in limited partnerships	4.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	$ 2,816	2,739	$ 2,576
Pension Benefits | Total Plan Assets Including Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	2,816	2,739
Pension Benefits | Total Plan Assets Including Net Asset Value | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	961	961
Pension Benefits | Total Plan Assets Including Net Asset Value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	934	956
Pension Benefits | Total Plan Assets Including Net Asset Value | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	8	9
Pension Benefits | Plan Assets At Fair Value | Total
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	1,903	1,926
Pension Benefits | Plan Assets At Fair Value | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	961	961
Pension Benefits | Plan Assets At Fair Value | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	934	956
Pension Benefits | Plan Assets At Fair Value | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	8	9
Pension Benefits | Total fixed maturities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	793	782
Pension Benefits | Total fixed maturities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	0	0
Pension Benefits | Total fixed maturities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	785	773
Pension Benefits | Total fixed maturities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	8	9
Pension Benefits | Corporate bonds and other
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	653	652
Pension Benefits | Corporate bonds and other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Corporate bonds and other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	645	643
Pension Benefits | Corporate bonds and other | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	8	9
Pension Benefits | States, municipalities and political subdivisions
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	30	32
Pension Benefits | States, municipalities and political subdivisions | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | States, municipalities and political subdivisions | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	30	32
Pension Benefits | States, municipalities and political subdivisions | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Asset-backed
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	110	98
Pension Benefits | Asset-backed | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Asset-backed | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	110	98
Pension Benefits | Asset-backed | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	942	922
Pension Benefits | Equity Securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	801	785
Pension Benefits | Equity Securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	141	137
Pension Benefits | Equity Securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	47	75
Pension Benefits | Short-term Investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	47	37
Pension Benefits | Short-term Investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets		38
Pension Benefits | Short-term Investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Fixed income mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	111	139
Pension Benefits | Fixed income mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	111	139
Pension Benefits | Fixed income mutual funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Fixed income mutual funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Other Assets
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	10	8
Pension Benefits | Other Assets | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	2
Pension Benefits | Other Assets | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	8	8
Pension Benefits | Other Assets | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total plan assets
Pension Benefits | Equity securities | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	20
Pension Benefits | Limited partnerships | Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Total plan assets	$ 893	$ 813