Insurance (Guarantees Related to Annuity Contracts) (Details) - Variable Annuity Guarantees - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Guaranteed Death Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 104,974	$ 105,061
Separate account value	100,115	100,043
Net amount at risk	$ 6,473	$ 5,200
Average attained age of contract holders	68 years	68 years
Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 60,458	$ 59,691
Separate account value	59,330	58,511
Net amount at risk	$ 2,468	$ 2,330
Average attained age of contract holders	68 years	68 years