Fair Value (Reconciliation of Assets Measured at Fair Value on a Recurring Basis Using Level 3 Inputs) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 388	$ 359	$ 384	$ 311
Purchases	16	16	24	63
Sales	(15)	(147)	(16)	(151)
Net unrealized gains (losses) in accumulated other comprehensive income	1	7	(3)	12
Net realized losses in investment and other income	13	124	14	124
Balance at end of period	403	359	403	359
Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	79	46	74	42
Purchases	6	10	10	13
Sales	(2)	0	(2)	0
Net unrealized gains (losses) in accumulated other comprehensive income	1	1	2	2
Net realized losses in investment and other income	0	0	0	0
Balance at end of period	84	57	84	57
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	309	313	310	269
Purchases	10	6	14	50
Sales	(13)	(147)	(14)	(151)
Net unrealized gains (losses) in accumulated other comprehensive income	0	6	(5)	10
Net realized losses in investment and other income	13	124	14	124
Balance at end of period	$ 319	$ 302	$ 319	$ 302