Employment Benefit Plans Plan Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Equity securities exceeding 10 percent of plan assets	three	three
Percent of total assets that equity securities exceeding 10 percent of plan assets represent	10.00%	10.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	58.00%	51.00%
Accrued dividend and interest receivable, Less than	$ 1,000,000	$ 1,000,000
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,672,000,000	2,336,000,000	$ 2,669,000,000
Pension Benefits | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,631,000,000	2,302,000,000
Pension Benefits | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	41,000,000	34,000,000
Pension Benefits | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Cash and equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	32,000,000	21,000,000
Pension Benefits | Cash and equivalents | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,000,000	1,000,000
Pension Benefits | Cash and equivalents | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	30,000,000	20,000,000
Pension Benefits | Cash and equivalents | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,518,000,000	1,895,000,000
Pension Benefits | Equity Securities | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,518,000,000	1,895,000,000
Pension Benefits | Equity Securities | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Equity Securities | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Government obligations
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	111,000,000	403,000,000
Pension Benefits | Government obligations | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	111,000,000	403,000,000
Pension Benefits | Government obligations | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Government obligations | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Other fixed maturity securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	11,000,000	14,000,000
Pension Benefits | Other fixed maturity securities | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Other fixed maturity securities | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	11,000,000	14,000,000
Pension Benefits | Other fixed maturity securities | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Investment funds and other
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	3,000,000
Pension Benefits | Investment funds and other | Level 1 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	3,000,000
Pension Benefits | Investment funds and other | Level 2 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	0
Pension Benefits | Investment funds and other | Level 3 Inputs
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	$ 0	$ 0