Insurance (Guarantees Related to Universal and Variable Life Contracts) (Details) - Secondary Guarantees - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Universal Life
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 5,917	$ 5,957
Net amount at risk (6)	$ 70,588	$ 71,124
Average attained age of policyholders	66 years	66 years
Variable Life
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 957	$ 1,133
Net amount at risk (6)	$ 12,024	$ 12,082
Average attained age of policyholders	46 years	45 years