Variable Annuity and Insurance Guarantees (Separate Account Balance by Type) (Details 5) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Mutual funds
Distribution of separate account balances by asset type for variable annuity contracts providing guaranteed benefits:
Total mutual funds	$ 74,676	$ 69,090
Equity
Distribution of separate account balances by asset type for variable annuity contracts providing guaranteed benefits:
Total mutual funds	46,038	40,622
Bond
Distribution of separate account balances by asset type for variable annuity contracts providing guaranteed benefits:
Total mutual funds	23,529	23,142
Other
Distribution of separate account balances by asset type for variable annuity contracts providing guaranteed benefits:
Total mutual funds	$ 5,109	$ 5,326