Schedule VI Supplementary Information Concerning Property and Casualty Insurance Operations (Details) - Property and Casualty Insurance Products - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Discount Deducted From Liabilities	$ 410	$ 483	$ 523
Losses and Loss Adjustment Expenses Incurred Related to: Current Year	7,381	6,990	6,647
Losses and Loss Adjustment Expenses Incurred Related to: Prior Year	(41)	457	250
Paid Losses and Loss Adjustment Expenses	$ 6,579	$ 6,968	$ 6,719
Weighted average interest rate	3.06%	3.11%	3.24%