Accumulated Other Comprehensive Income Loss Level 4 -AOCI Rollforward (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax Cuts and Jobs Act of 2017, Reclassification from AOCI to Retained Earnings		$ 88
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 13,494	13,494
OCI, before Reclassifications		(920)	$ 157
Amounts reclassified from AOCI		23	(27)
OCI, net of tax		(897)	130
Ending balance		13,143	17,009
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		169	75
Net Unrealized Gain on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change net of income taxes				$ 273
Adjusted balance, beginning of period				2,204
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,931	1,931	1,276
OCI, before Reclassifications	83	(882)	160
Amounts reclassified from AOCI		27	(23)
OCI, net of tax		(855)	137
Ending balance		1,349	1,413
OTTI Losses in OCI
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change net of income taxes				0
Adjusted balance, beginning of period				(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(3)	(3)	(3)
OCI, before Reclassifications		(2)	(1)
Amounts reclassified from AOCI		0	0
OCI, net of tax		(2)	(1)
Ending balance		(5)	(4)
Net Gain on Cash Flow Hedging Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change net of income taxes				2
Adjusted balance, beginning of period				20
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	18	18	76
OCI, before Reclassifications		(31)	(4)
Amounts reclassified from AOCI		(13)	(14)
OCI, net of tax		(44)	(18)
Ending balance		(24)	58
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change net of income taxes				4
Adjusted balance, beginning of period				38
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	34	34	6
OCI, before Reclassifications		(6)	2
Amounts reclassified from AOCI		0	0
OCI, net of tax		(6)	2
Ending balance		32	8
Pension and Other Postretirement Plan Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change net of income taxes				(284)
Adjusted balance, beginning of period				(1,601)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,317)	(1,317)	(1,692)
OCI, before Reclassifications		1	0
Amounts reclassified from AOCI		9	10
OCI, net of tax		10	10
Ending balance		(1,591)	(1,682)
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of accounting change net of income taxes				(5)	$ 0
Adjusted balance, beginning of period				$ 658	$ (337)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	663	663	(337)
Ending balance		$ (239)	$ (207)
Equity Securities [Member] | Net Unrealized Gain on Securities
Increase (Decrease) in Stockholders' Equity [Roll Forward]
OCI, before Reclassifications	$ 93