Insurance (Guarantees Related to Annuity Contracts) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Variable Annuity Guarantees: | Guaranteed Death Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 181,504	$ 177,895
Separate account value	153,699	150,118
Net amount at risk	$ 7,740	$ 8,679
Average attained age of contractholders	67 years	66 years
Variable Annuity Guarantees: | Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 91,461	$ 89,839
Separate account value	88,067	86,355
Net amount at risk	$ 3,647	$ 3,834
Average attained age of contractholders	66 years	66 years
Other Annuity Guarantees: | Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 1,382	$ 1,393
Net amount at risk	$ 486	$ 490
Average attained age of contractholders	51 years	50 years