Insurance (Liabilities for Unpaid Claims - Methodology) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-duration Insurance Contract, Discounted Liability, Discount	$ 1,314
Group Long-Term Disability
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Amount	6,000	$ 6,000
Short-duration Insurance Contract, Discounted Liability, Discount	1,300	1,300
Short-duration Insurance Contracts, Discounted Liabilities, Interest Accretion	$ 509	510	$ 565
Group Long-Term Disability | Minimum
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	3.00%
Group Long-Term Disability | Maximum
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	8.00%
Group Life - Term | Asia
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Amount	$ 733	756
Short-duration Insurance Contract, Discounted Liability, Discount	61	57
Short-duration Insurance Contracts, Discounted Liabilities, Interest Accretion	$ 19	$ 26	$ 22
Group Life - Term | Minimum | Asia
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	3.00%
Group Life - Term | Maximum | Asia
Liability for Claims and Claims Adjustment Expense [Line Items]
Short-Duration Contracts, Discounted Liabilities, Discount Rate	7.00%