Commitments and Contingent Liabilities Commitments and Contingent Liabilities (Assurance IQ Contingent Consideration Liability Narrative) (Details) - USD ($)	3 Months Ended		36 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2022	Dec. 31, 2019	Oct. 31, 2019	Sep. 04, 2019
Business Acquisition [Line Items]
Net income (loss)	$ (270,000,000)	$ 937,000,000
Share price (usd per share)						$ 83.71
Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Contingent consideration, liability	$ 47,000,000			$ 105,000,000
Cash | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Equity interest in acquiree					25.00%
Common Stock | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Equity interest in acquiree					75.00%
Condition Three | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Contingent liability, stock based compensation component				$ 900,000,000
Condition Four - Quotient - Denominator | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Consideration payable, cash and equity interests					$ 400,000,000
Condition Four - Multiplier | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Consideration payable, cash and equity interests					1,150,000,000
Subsequent Event | Condition One | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Net income (loss)			$ 900,000,000
Subsequent Event | Condition Four - Quotient - Numerator | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Net income (loss)			900,000,000
Minimum | Condition One | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Consideration payable, cash and equity interests					0
Minimum | Subsequent Event | Condition Two | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Net income (loss)			1,300,000,000
Minimum | Subsequent Event | Condition Three | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Net income (loss)			900,000,000
Maximum | Condition Two | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Consideration payable, cash and equity interests					$ 1,150,000,000
Maximum | Subsequent Event | Condition Three | Acquisition of Assurance IQ, Inc.
Business Acquisition [Line Items]
Net income (loss)			$ 1,300,000,000