Reinsurance (Effects of Affiliated Reinsurance on Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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
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
Assumed | Affiliated Entity [Member]
Assets:
Premiums, reinsurance and other receivables	34	23
Liabilities:
Policyholder account balances	436	741
Other Policyholder Funds	1,683	1,677
Other Liabilities	(8)	11
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
Ceded | Affiliated Entity [Member]
Assets:
Premiums, reinsurance and other receivables	3,254	3,382
Liabilities:
Policyholder account balances	0	0
Other Policyholder Funds	0	0
Other Liabilities	$ 401	$ 578