Insurance (Guarantees Related to Annuity Contracts) (Details) - Variable Annuity Guarantees - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Guaranteed Death Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 98,832	$ 92,794
Separate account value	94,126	88,065
Net amount at risk	$ 7,579	$ 10,945
Average attained age of contract holders	69 years	69 years
Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 56,695	$ 53,330
Separate account value	55,608	52,225
Net amount at risk	$ 3,131	$ 3,903
Average attained age of contract holders	69 years	68 years