Insurance (Guarantees Related to Universal and Variable Life Contracts) (Details) - Universal and Variable Life Contracts - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Secondary Guarantees
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (1), (3)	$ 9,089	$ 9,036
Net amount at risk (7)	$ 65,541	$ 66,956
Average attained age of policyholders	57 years	56 years
Paid-Up Guarantees
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (1), (3)	$ 3,136	$ 3,207
Net amount at risk (7)	$ 16,060	$ 16,615
Average attained age of policyholders	64 years	63 years