Claim and Claim Adjustment Expense Reserves Short Duration Contracts – Net Cumulative Paid Claim and Claim Adjustment Expenses - International - Hardy (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	$ 4,167	$ 4,089	$ 4,355
Liability for Unpaid Claims and Claims Adjustment Expense, Net	18,249	18,576	18,927	$ 19,117
Hardy [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	720
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	310
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	3
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense	7
Liability for Unpaid Claims and Claims Adjustment Expense, Net	320
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2007 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	14	14	14	14	$ 3
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net					12
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2008 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	11	10	10	14	3
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net					14
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2009 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	(4)	(4)	(4)	(2)	1
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net					12
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2010 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	45	43	41	34	19
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net					36
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2011 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	127	123	119	80	29
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net					121
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2012 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	104	107	98	78	14
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net					$ 102
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2013 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	125	119	100	$ 37
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2014 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	139	121	$ 55
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	97	$ 29
Hardy [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member]
Short Duration Contracts Net Cumulative Paid Claim Adjustment Expenses [Line Items]
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 62