Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Corporate and other bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 465	$ 478
Corporate and other bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate and other bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	455	463
Corporate and other bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	15	$ 15
States, municipalities and political subdivisions [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	106	80
States, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
States, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	106	80
States, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Residential mortgage-backed [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	133	123
Residential mortgage-backed [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Residential mortgage-backed [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	133	123
Residential mortgage-backed [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Commercial Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	69	75
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	69	75
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other asset-backed [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	12
Other asset-backed [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other asset-backed [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	12
Other asset-backed [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Total asset-backed [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	213	210
Total asset-backed [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Total asset-backed [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	213	210
Total asset-backed [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	25
U.S. Treasury and obligations of government-sponsored enterprises [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	25
U.S. Treasury and obligations of government-sponsored enterprises [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
U.S. Treasury and obligations of government-sponsored enterprises [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fixed Maturities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	784	793
Fixed Maturities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	25
Fixed Maturities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	774	753
Fixed Maturities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	15	15
Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	443	507
Equity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	336	389
Equity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	107	118
Equity securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	8
Derivative Financial Instruments, Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Short-term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	52	134
Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24	33
Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28	101
Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	812	865
Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	516	562
Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	296	303	322
Private Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	123	113
Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	123	113	114
Total limited partnerships [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	935	978
Total limited partnerships [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Total limited partnerships [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	516	562
Total limited partnerships [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	419	416	436
Other assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	52	30
Other assets [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other assets [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	52	30
Other assets [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13
Cash [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		13
Cash [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Cash [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Total assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,267	2,456
Total assets [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	361	461
Total assets [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,477	1,564
Total assets [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 429	$ 431	$ 459