Fair Value (Financial Instruments Carried at Other Than Fair Value) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Assets
Policy loans	$ 11,072	$ 11,028
Liabilities
Collateral financing arrangements	1,235	4,071
Junior subordinated debt securities	3,169	3,169
Separate account liabilities	320,455	308,620
Carrying Value
Assets
Mortgage loans	76,834	73,843
Policy loans	11,072	11,028
Real estate joint ventures	9	17
Other limited partnership interests	323	384
Other invested assets	538	506
Premiums, reinsurance and other receivables	4,614	5,140
Other assets	325	237
Liabilities
Policyholder account balances	127,341	124,475
Long-term debt	19,473	16,459
Collateral financing arrangements	1,235	4,071
Junior subordinated debt securities	3,169	3,169
Other liabilities	3,158	2,028
Separate account liabilities	125,154	119,498
Estimated Fair Value
Assets
Mortgage loans	78,792	75,129
Policy loans	13,142	13,015
Real estate joint ventures	43	69
Other limited partnership interests	314	413
Other invested assets	537	505
Premiums, reinsurance and other receivables	4,725	5,161
Other assets	360	269
Liabilities
Policyholder account balances	131,171	127,833
Long-term debt	21,396	18,016
Collateral financing arrangements	957	3,775
Junior subordinated debt securities	4,329	3,982
Other liabilities	3,159	2,028
Separate account liabilities	125,154	119,498
Estimated Fair Value | Level 1
Assets
Mortgage loans	0	0
Policy loans	0	0
Real estate joint ventures	0	0
Other limited partnership interests	0	0
Other invested assets	149	145
Premiums, reinsurance and other receivables	0	0
Other assets	0	0
Liabilities
Policyholder account balances	0	0
Long-term debt	0	0
Collateral financing arrangements	0	0
Junior subordinated debt securities	0	0
Other liabilities	0	0
Separate account liabilities	0	0
Estimated Fair Value | Level 2
Assets
Mortgage loans	0	0
Policy loans	1,111	1,115
Real estate joint ventures	0	0
Other limited partnership interests	0	0
Other invested assets	0	0
Premiums, reinsurance and other receivables	1,517	1,982
Other assets	245	198
Liabilities
Policyholder account balances	0	0
Long-term debt	21,396	18,016
Collateral financing arrangements	0	0
Junior subordinated debt securities	4,329	3,982
Other liabilities	2,623	1,540
Separate account liabilities	125,154	119,498
Estimated Fair Value | Level 3
Assets
Mortgage loans	78,792	75,129
Policy loans	12,031	11,900
Real estate joint ventures	43	69
Other limited partnership interests	314	413
Other invested assets	388	360
Premiums, reinsurance and other receivables	3,208	3,179
Other assets	115	71
Liabilities
Policyholder account balances	131,171	127,833
Long-term debt	0	0
Collateral financing arrangements	957	3,775
Junior subordinated debt securities	0	0
Other liabilities	536	488
Separate account liabilities	$ 0	$ 0