Benefit Plans (Reconciliation of Level 3 Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Corporate and other bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	$ 478
Fair value of plan assets at December 31	465	$ 478
Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	793
Fair value of plan assets at December 31	784	793
Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	507
Fair value of plan assets at December 31	443	507
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	865
Fair value of plan assets at December 31	812	865
Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	113
Fair value of plan assets at December 31	123	113
Total limited partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	978
Fair value of plan assets at December 31	935	978
Total assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	2,456
Fair value of plan assets at December 31	2,267	2,456
Fair Value, Inputs, Level 3 [Member] | Corporate and other bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	15	15
Defined Benefit Plan, Actual Return on Plan Assets Still Held	0	0
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	0
Defined Benefit Plan, Purchases, Sales, and Settlements	0	0
Defined Benefit Plan, Net transfers into (out of) Level 3	(5)	0
Fair value of plan assets at December 31	10	15
Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	15	15
Defined Benefit Plan, Actual Return on Plan Assets Still Held	0	0
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	0
Defined Benefit Plan, Purchases, Sales, and Settlements	0	0
Defined Benefit Plan, Net transfers into (out of) Level 3	(5)	0
Fair value of plan assets at December 31	10	15
Fair Value, Inputs, Level 3 [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	0	8
Defined Benefit Plan, Actual Return on Plan Assets Still Held		0
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period		0
Defined Benefit Plan, Purchases, Sales, and Settlements		(8)
Defined Benefit Plan, Net transfers into (out of) Level 3		0
Fair value of plan assets at December 31	0	0
Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	303	322
Defined Benefit Plan, Actual Return on Plan Assets Still Held	18	19
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	0
Defined Benefit Plan, Purchases, Sales, and Settlements	(25)	(38)
Defined Benefit Plan, Net transfers into (out of) Level 3	0	0
Fair value of plan assets at December 31	296	303
Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	113	114
Defined Benefit Plan, Actual Return on Plan Assets Still Held	9	19
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	0
Defined Benefit Plan, Purchases, Sales, and Settlements	1	(20)
Defined Benefit Plan, Net transfers into (out of) Level 3	0	0
Fair value of plan assets at December 31	123	113
Fair Value, Inputs, Level 3 [Member] | Total limited partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	416	436
Defined Benefit Plan, Actual Return on Plan Assets Still Held	27	38
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	0
Defined Benefit Plan, Purchases, Sales, and Settlements	(24)	(58)
Defined Benefit Plan, Net transfers into (out of) Level 3	0	0
Fair value of plan assets at December 31	419	416
Fair Value, Inputs, Level 3 [Member] | Total assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at January 1	431	459
Defined Benefit Plan, Actual Return on Plan Assets Still Held	27	38
Defined Benefit Plan, Actual Return on Plan Assets Sold During Period	0	0
Defined Benefit Plan, Purchases, Sales, and Settlements	(24)	(66)
Defined Benefit Plan, Net transfers into (out of) Level 3	(5)	0
Fair value of plan assets at December 31	$ 429	$ 431