Insurance (Guarantees Related to Annuity Contracts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Variable Annuity Guarantees: | Guaranteed Death Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 66,724	$ 66,176
Separate account value	45,431	43,359
Net amount at risk	$ 1,238	$ 1,842
Average attained age of contractholders	65 years	64 years
Variable Annuity Guarantees: | Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 26,223	$ 25,335
Separate account value	24,336	23,330
Net amount at risk	$ 525	$ 521
Average attained age of contractholders	65 years	65 years
Other Annuity Guarantees: | Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 1,424	$ 1,393
Net amount at risk	$ 569	$ 490
Average attained age of contractholders	50 years	50 years