Claim and Claim Adjustment Expense Reserves Short Duration Contracts - Consolidated Reconciliation (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 18,249	$ 18,576	$ 18,927	$ 19,117
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	4,094
Total Gross Carried Claim and Claim Adjustment Expense Reserves	22,343	22,663	$ 23,271	$ 24,089
Specialty [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	5,404	5,568
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	745
Total Gross Carried Claim and Claim Adjustment Expense Reserves	6,149	6,269
Commercial [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	8,305	8,576
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	589
Total Gross Carried Claim and Claim Adjustment Expense Reserves	8,894	9,183
International [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	1,201	1,219
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	127
Total Gross Carried Claim and Claim Adjustment Expense Reserves	1,328	1,347
Corporate and Other [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	230	283
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	2,384
Total Gross Carried Claim and Claim Adjustment Expense Reserves	2,614	2,644
Life and Group Non-Core [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,109	2,930
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	249
Total Gross Carried Claim and Claim Adjustment Expense Reserves	$ 3,358	$ 3,220