Basis of Presentation and Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended			9 Months Ended
	Aug. 22, 2018	May 31, 2018	Jan. 01, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fee income				$ 344		$ 291	$ 994	$ 855
TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect			$ (88)
Equity securities, AFS				0			0		$ 1,012
Other revenues				29		24	73	66
Total revenues subject to updated guidance				373		315	1,067	921
Operating Expense [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Distribution Costs						48		140
Net Unrealized Gain on Securities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change net of income taxes									273
Net Unrealized Gain on Securities | Equity Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity securities, AFS			1,000
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect					$ (193)
Corporate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fee income				15		1	21	2
Other revenues				6		0	8	0
Continuing Operations [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
TaxCutsAndJobsActOf2017ReclassificationFromAociToRetainedEarningsTaxEffect			(105)
Installment billing fees | Operating Segments | Commercial Lines
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fee income				9		9	26	28
Installment billing fees | Operating Segments | Personal Lines
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fee income				10		11	30	33
Insurance servicing revenues | Operating Segments | Personal Lines
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other revenues				24		24	66	66
Administrative services | Operating Segments | Group Benefits
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fee income				43		19	131	57
Advisor, distribution and other management fees | Operating Segments | Mutual Funds
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fee income				245		229	722	660
Other fees | Operating Segments | Mutual Funds
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Fee income				21		$ 22	63	$ 75
Maximum [Member] | Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] | Other Income [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Discontinued Operation, Period of Continuing Involvement after Disposal		24 months
Equity Securities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change net of income taxes			83
Equity securities, AFS									$ 1,012
Shadow DAC [Member] | Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change net of income taxes			$ 10
The Navigators Group, Inc. [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Business Acquisition, Share Price	$ 70
Business Combination, Consideration Transferred	$ 2,100