Share-Based Payments (Weighted Average Remaining Contractual Term and Aggregate Intrinsic Value of Stock Options Outstanding, Vested and Expected to Vest, and Exercisable) (Details) - Employee stock options $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Weighted Average Remaining Contractual Term	4 years 6 months 10 days
Exercisable, Weighted Average Remaining Contractual Term	3 years 8 months 23 days
Outstanding, Aggregate Intrinsic Value	$ 92
Exercisable, Aggregate Intrinsic Value	$ 92
Assurance IQ
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Weighted Average Remaining Contractual Term	8 years 5 months 19 days
Exercisable, Weighted Average Remaining Contractual Term	8 years 8 months 8 days
Outstanding, Aggregate Intrinsic Value	$ 51
Exercisable, Aggregate Intrinsic Value	$ 3