Income Taxes - Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets [Abstract]
Employee and retiree benefit plans	$ 279	$ 481
Other insurance and contractholder liabilities	352	460
Net operating losses	105	128
Other accrued liabilities	101	166
Other	91	140
Deferred tax assets before valuation allowance	928	1,375
Valuation allowance for deferred tax assets	(72)	(87)
Deferred tax assets, net of valuation allowance	856	1,288
Deferred tax liabilities [Abstract]
Depreciation and amortization	496	781
Unrealized appreciation (depreciation) on investments and foreign currency translation	102	149
Other	225	54
Total deferred tax liabilities	823	984
Net deferred income tax assets	33	$ 304
Foreign [Member]
Deferred tax liabilities [Abstract]
Total deferred tax liabilities	$ 175