Insurance (Reconciliation of Disclosure to Liability) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 12,349
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	661
Total unpaid claims and allocated claims adjustment expense	13,010
Unallocated claims adjustment expenses	107
Discounting	(1,328)
Liability for unpaid claims and claim adjustment liabilities - short-duration	11,789
Liability for unpaid claims and claim adjustment liabilities - long-duration	5,305
Liability for Claims and Claims Adjustment Expense	17,094	$ 16,157	$ 9,669	$ 9,525
U.S.
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	10,460
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	189
Latin America
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	367
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	8
Group Life - Term
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	1,903
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	16
Group Life - Term | Asia
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	552
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	261
Group Long-Term Disability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	7,135
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	95
Discounting	1,300	$ 1,300
Property & Casualty - Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	1,196
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	73
Property & Casualty - Home
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	226
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	5
Protection Life
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	280
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	4
Protection Health
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	87
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	4
Other insurance lines - all segments combined
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	970
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	$ 203