Insurance (Guarantees Related to Annuity Contracts) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Variable Annuity Guarantees: | Guaranteed Death Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 66,814	$ 66,176
Separate account value	45,046	43,359
Net amount at risk	$ 1,401	$ 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	$ 26,098	$ 25,335
Separate account value	24,179	23,330
Net amount at risk	$ 568	$ 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	$ 1,432	$ 1,393
Net amount at risk	$ 580	$ 490
Average attained age of contractholders	50 years	50 years