Insurance (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Analysis of changes in the liability for losses and loss adjustment expenses, net of reinsurance
Balance at beginning of period				$ 5,645				$ 4,288	$ 5,645	$ 4,288		$ 4,129
Provision for losses and LAE occurring in the current year									2,662	2,488		2,055
Net increase (decrease) in the provision for claims of prior years:
Provision for claims of prior years related to special A&E charges and other	$ (5)	$ 55	$ (10)	$ (7)	$ 10	$ 13	$ 14	$ (31)	33	6
Total losses and LAE incurred									2,695	2,494		2,040
Payments for losses and LAE of:
Current year									(828)	(789)		(739)
Prior years									(1,575)	(1,340)		(1,131)
Total payments									(2,403)	(2,129)		(1,870)
Reserves of businesses acquired									0	1,028	[1]	0
Foreign currency translation and other									(11)	(36)		(11)
Balance at end of period	5,926				5,645				5,926	5,645		4,288
Add back reinsurance recoverables, net of allowance	2,201				2,227				2,201	2,227		2,122
Gross unpaid losses and LAE included in the balance sheet	$ 8,127				$ 7,872				8,127	7,872		6,410
Special A&E Charges [Member]
Net increase (decrease) in the provision for claims of prior years:
Provision for claims of prior years related to special A&E charges and other									67	24		54
Other [Member]
Net increase (decrease) in the provision for claims of prior years:
Provision for claims of prior years related to special A&E charges and other									$ (34)	$ (18)		$ (69)

[1] Reflects the acquisition of Summit in April 2014 (see Note B — “Acquisitions and Sale of Businesses”).