Employment Benefit Plans Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Significant Concentrations of Risk, securities	four		three
Defined Benefit Plan, Actual Plan Asset Allocations	56.00%		47.00%
Accrued dividend and interest receivable, Less than	$ 1		$ 1
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,333	[1]	2,289	[2]
Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,148	[1],[3]	2,082	[2],[4]
Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	185	[1],[3]	207	[2],[4]
Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[1],[3]	0	[2],[4]
Pension Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	1		167
Pension Plan [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	1	[3]	3	[4]
Pension Plan [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3]	164	[4]
Pension Plan [Member] | Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3]	0	[4]
Pension Plan [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,139	[5]	2,060	[6]
Pension Plan [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	2,139	[3],[5]	2,060	[4],[6]
Pension Plan [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3],[5]	0	[4],[6]
Pension Plan [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3],[5]	0	[4],[6]
Pension Plan [Member] | Government Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	164		12
Pension Plan [Member] | Government Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3]	0	[4]
Pension Plan [Member] | Government Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	164	[3]	12	[4]
Pension Plan [Member] | Government Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3]	0	[4]
Pension Plan [Member] | Other fixed maturity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	21		31
Pension Plan [Member] | Other fixed maturity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3]	0	[4]
Pension Plan [Member] | Other fixed maturity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	21	[3]	31	[4]
Pension Plan [Member] | Other fixed maturity securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3]	0	[4]
Pension Plan [Member] | Investment funds and other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	8		19
Pension Plan [Member] | Investment funds and other [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	8	[3]	19	[4]
Pension Plan [Member] | Investment funds and other [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	0	[3]	0	[4]
Pension Plan [Member] | Investment funds and other [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets Excluding Accrued Dividend And Interest Receivable	$ 0	[3]	$ 0	[4]

[1] Excludes less than $1 million accrued for dividend and interest receivable.

[2] Excludes less than $1 million accrued for dividend and interest receivable.

[3] See Note 2 to the Consolidated Financial Statements under the heading “Fair Value Measurements” for a definition of each of these levels of inputs.

[4] See Note 2 to the Consolidated Financial Statements under the heading “Fair Value Measurements” for a definition of each of these levels of inputs.

[5] As of December 31, 2016, four equity securities each exceeded 10 percent of total plan assets. These investments represent approximately 56 percent of total plan assets.

[6] As of December 31, 2015, three equity securities each exceeded 10 percent of total plan assets. These investments represented approximately 47 percent of total plan assets.