Reinsurance (Effects of Reinsurance on Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Premiums, reinsurance and other receivables (includes $3 and $2, respectively, relating to variable interest entities)	$ 18,423	$ 15,445
Deferred Policy Acquisition Costs and Present Value of Future Insurance Profits, Net	18,419	17,590	$ 17,430
Total assets	36,842	33,035
Liabilities
Liability for Future Policy Benefits	177,974	166,636
Policyholder Contract Deposits	182,518	172,486	$ 165,130
Other Policy-Related Balances	15,515	13,402
Other Liabilities	23,982	23,735
Total liabilities	399,989	376,259
Direct Reinsurance [Member]
Assets
Premiums, reinsurance and other receivables (includes $3 and $2, respectively, relating to variable interest entities)	6,300	5,927
Deferred Policy Acquisition Costs and Present Value of Future Insurance Profits, Net	18,350	17,878
Total assets	24,650	23,805
Liabilities
Liability for Future Policy Benefits	174,694	165,121
Policyholder Contract Deposits	182,226	171,961
Other Policy-Related Balances	14,962	13,071
Other Liabilities	17,077	18,815
Total liabilities	388,959	368,968
Assumed Reinsurance [Member]
Assets
Premiums, reinsurance and other receivables (includes $3 and $2, respectively, relating to variable interest entities)	866	543
Deferred Policy Acquisition Costs and Present Value of Future Insurance Profits, Net	398	16
Total assets	1,264	559
Liabilities
Liability for Future Policy Benefits	3,280	1,515
Policyholder Contract Deposits	293	527
Other Policy-Related Balances	520	324
Other Liabilities	1,896	405
Total liabilities	5,989	2,771
Ceded Reinsurance [Member]
Assets
Premiums, reinsurance and other receivables (includes $3 and $2, respectively, relating to variable interest entities)	11,257	8,975
Deferred Policy Acquisition Costs and Present Value of Future Insurance Profits, Net	(329)	(304)
Total assets	10,928	8,671
Liabilities
Liability for Future Policy Benefits	0	0
Policyholder Contract Deposits	(1)	(2)
Other Policy-Related Balances	33	7
Other Liabilities	5,009	4,515
Total liabilities	$ 5,041	$ 4,520