Insurance (Guarantees Related to Universal and Variable Life Contracts) (Details) - Universal and Variable Life Contracts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Secondary Guarantees
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 9,036	$ 8,363
Net amount at risk (7)	$ 66,956	$ 70,225
Average attained age of policyholders	56 years	55 years
Paid-Up Guarantees
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 3,207	$ 3,337
Net amount at risk (7)	$ 16,615	$ 17,785
Average attained age of policyholders	63 years	62 years