Insurance (Guarantees Related to Universal and Variable Life Contracts) (Details) - Secondary Guarantees - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Universal Life
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 6,056	$ 6,099
Net amount at risk (6)	$ 72,642	$ 73,131
Average attained age of policyholders	65 years	65 years
Variable Life
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 1,045	$ 954
Net amount at risk (6)	$ 12,729	$ 13,040
Average attained age of policyholders	45 years	45 years