Insurance (Guarantees Related to Universal and Variable Life Contracts) (Details) - Secondary Guarantees - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Universal Life [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 6,244	$ 6,216
Net amount at risk (6)	$ 75,304	$ 76,216
Average attained age of policyholders	64 years	63 years
Variable Life [Member]
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 1,021	$ 960
Net amount at risk (6)	$ 13,848	$ 14,757
Average attained age of policyholders	44 years	43 years