Reinsurance (Effects of Reinsurance on Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effects of Reinsurance [Line Items]
Deposit Contracts, Liabilities	$ 198	$ 1
Assets:
Premiums, reinsurance and other receivables	12,918	13,853
Deferred policy acquisition costs and value of business acquired	5,623	6,339	$ 5,777
Liabilities:
Future policy benefits	35,715	32,752
Policyholder account balances	37,069	36,579
Other Policyholder Funds	2,720	2,712
Other Liabilities	4,419	5,445
Direct
Assets:
Premiums, reinsurance and other receivables	367	1,161
Liabilities:
Policyholder account balances	36,359	35,838
Other Policyholder Funds	1,037	1,035
Other Liabilities	3,724	4,525
Assumed
Assets:
Premiums, reinsurance and other receivables	43	23
Liabilities:
Policyholder account balances	710	741
Other Policyholder Funds	1,683	1,677
Other Liabilities	(6)	13
Ceded
Assets:
Premiums, reinsurance and other receivables	12,508	12,669
Liabilities:
Policyholder account balances	0	0
Other Policyholder Funds	0	0
Other Liabilities	$ 701	$ 907