Insurance (Guarantees Related to Annuity Contracts) (Details) - Variable Annuity Guarantees - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Guaranteed Death Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 105,061	$ 106,590
Separate account value	100,043	101,991
Net amount at risk	$ 5,200	$ 6,763
Average attained age of contract holders	68 years	67 years
Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 59,691	$ 61,340
Separate account value	58,511	60,016
Net amount at risk	$ 2,330	$ 3,116
Average attained age of contract holders	68 years	67 years